Notes on the Staminate Cone of "Larix leptolepis"

Notes on the Staminate Cone of "Larix leptolepis"Author(s): Joseph DoyleSource: Proceedings of the Royal Irish Academy. Section B: Biological, Geological, andChemical Science, Vol. 37 (1924 - 1927), pp. 154-169Published by: Royal Irish AcademyStable URL: http://www.jstor.org/stable/20490325 .

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[ 154 ]

XVIII.

NOTES ON THE STAMINATE CONE OF LARIX LEIPTOLEPIS.

BY JOSEPH DOYLE, Professor of Botany, University College, Dublin.

(PLATES X-XII.)

[Read MAY 10. Published AuGUST 31, 1926.]

A GENERAL account of the morphology of Larix leptolepis was published in 1918 (7). From the facts there presented the general conclusion was arrived at, that an exceedingly close relationship exists between the goenera Larix and Pseudotsuga. That conclusion was based in the first place on certain long-established data: (a) the absence of wings on the pollen; (b) the anatomical work of Jeffrey (11), sub-dividing the Abietineae into

Pineae and Abieteae, thus removing Larix from proximity to Cedrus., and

associating it with Pinus, Picea, and Pseudotsuga; (c) the extraordinary closeness of the wood anatomy of the two forms in question, as brought out clearly by Bailey (1) [cf. also Stopes (23)]; and in the second place on the fact that, as reported in 1918, the ovular and femalle gametophyte structures of Lanrx are almost an.exact replica of those earlier described

by Lawson (17) for Pseudotsmga, particular interest attaching to the peculiar pollen-receiving device of both genera. This relationship is not recognised by the older systematists. Even as recently as 1924 we find, in Hutchinson's (10) interesting articles in the Kew Bulletin, that Larix and Cedrus are still bracketed together.

In the intervals of other work since 1918 some further facts have accumulated, a few of which seemed worthy of record. These deal, not with systematics, but with questions of general comparative morphology, and bear most directly on the morphology of the microstrobilus of Conifers.

GENERAL AND HISTORICAL.

The discussions which have raged round the morphology of the megastrobilus of Conifers have rather overshadowed the question of the morphology of the staminate one, but nevertheless that question has its own great interest. Leaving to one side, for the moment, the position of the staminate cone, we find that, though all are arranged on a similar

plan-a number of "microsporophylls" arranged round the axis-yet the



DOYLE-Note8 on the Staminate Cone of Larix leptoZlis. 155

microsporophylls" show great diversity. In the Abietineae the small,

spirally arranged scales carry two sacs on the under surface; in the Cupressineae and Taxodineae more than two; in the Arancarineae many sacs are attached distally to the scale, but not along its length; in the

Podocarps the Abietinean condition is commonly repeated, while in the Taxineae we have the peltate scale of Taexus, Torreya with four sporangia

below, and Cephalotaxus w-ith two or more. The scale in Ginkgo commonly

bears two but distally attached and pendent, as in the Araucarians. Is

it possible, then, strictly to homologize these types and relate them to any one primitive form? The point has been frequently debated and written upon, especially within recent times, two divergent claims appearing. On the one hand a more or less radially symmetrical stamen, carrying many

sacs distally, perhaps somewhat as in Taxus or the sporangiophore of Equisetum, is considered primitive; on the other the basal type is recognised in the stamen of the Abietineae.

Taking the first view, we find it based on a group of well-known facts. Thuas Coulter and Land (6) have described the development of seven areas in the stamen of Torreya taxifolia, of which only the four abaxial develop to sporangia, the three adaxial showing early disintegration and fasion to form a large adaxial resin cavity. Each of these three shows a distinct primary sporogenous cell, and their potential sporogenous character is claimed. The two lateral ones of the four abaxial were smaller in one case.

A progressive reduction from Taxus through Torreya6 to Cephalotaous seems an obvious suggestion. Further, they claim the presence in young stamens of Pinus laricio of two&resin cavities lateral to its two sporangia, in the same relation as the two smaller to the two middle larger ones in Torreya, thus extending the claim to conelude that the condition in the Abietineae is related by reduction to a primitive peltate stamen of the Taxus type. This claim is further supported by the statement of Miss Robertson (18) that in Torreyac caltifornica the staminate strobilus is commonly terminated by a peltate stamen, bearing four or even six or seven sacs symmetrically arranged, the resin cavities being absent. It is further

well known that Ginkgo carries two pendent sacs at the end of the staminal stalk, which swells then to a small protuberance containing two mucilage cavities or one by fusion. Miss Starr (22) investigated the development of these, describing their early stages as essentially sporogenous in character, early disintegration causing the formation of mucilage cavities. She thus agrees with Coulter and Land, and claims the possibility of a Taxus-like stamen being primitive in the Ginkgo phylum. This receives further support from the consideration that the living Ginkgo may have more than two sacs-sometimes as many as seven-and that in stamens attributed to fossil species of Ginkgo many sacs are common. It is, of course, recognised that the attribution of these fossil stamens to the Ginkgo phylum is doubtful, to say the least; but when presenting the evidence for the first view, it is

F2B21



156 Prooeedings of the Royal Irish Academy.

attractive to call attention, at any rate, to such a condition as is figured

for Baiera Milnsteria'a Presl., in Potonie-Gothan's Lehrbuch der Palaeo botanik, where a most perfect peltate stamen, with seven pendent sporangia, is attributed to this species, which comes from beds which are at least as

old as the Lias, and possibly the Rhaetic. If we add the many pende}nt

sacs of the Araucarineae, the many sacs of the Cupressineae and Taxodineae, and find that the group, the Cordaiteae, from which these forms were all, probably, in some way or other derived, has also many sporangia terminally atached to a staminal stalk, as is so well known in Cordaianthus, we must

admit that there is strong evidence in favour of the first view.

The evidence for the second view is not based on any such anatomical data, nor in many ways is it so definite. The general view-citations are hardly necessary-would seem to be that the radial arrangement of the Taxineae is rather unique and perhaps derived, an abaxial position of the sacs, carried thus, like the sporangia of the Superficiales among the Ferns, on the under surface of the leaf or microsporophyll, being the primitive condition among the rest of the Conifers. This, of course, is in accordance

with the obviously widespread appearance in the adult of that condition. Jeffrey and his school, however, insist upon it as a fact of great importance, that not only is the abaxial condition primitive, but that two is the primitive number of sacs in all the Coniferales and Ginkgo. This is in accordance with their well-known theory of the superior antiquity of the Abietineae over any other living Conifer group. They claim, not only that two is primitive for the Cupressineae and Taxodineae, groups which have a "late" origin from the Abietineae, but they also believe that two is the primitive number for the Araucarineae and the Taxineae, Cephalotaxus being con

sidered mueh less advanced than Taxs. Thus Eames (9) says: --'-As

possibly primitive features in the history of the male gametophyte (of the Araucarineae) the large number of microsporangia . . . have been cited.

As concerns the sporangia, the Abietineae and the Podocarpineae are the only tribes in which the number is strictly two. The Taxineae and the

Araucarineae universally have more. Among the Taxodineae and the

Cupressineae several genera, clearly among the more specialised within the groups, have three to several microsporangia: for example, Sequoia, Taxodium, Widdriingtonia, Juniperus. " le goes on to agree with

Sinnott (21), who, he says, "shows the primitive character of the Podo

carpineae, emphasizing . . . their Abietinean affinities and their close

relationship to the Taxineae, which he considers a specialised branch from the group. This presents another instance of multiplication of sporangia, the two of the Podocarps becoming several in their recent branch the

Taxads. Further, the microsporangia of the primitive Ginkgo are two. Hence the occurrence of microsporangia in greater number than two among

the Conifers seems to be a feature of recent specialisation, and the

Araucarians cannot on that account be considered primitive" (p. 17).



DOYLE -Yotes on the Staminate Cone of Larix leptolepis 1>7

Sinnott (21) also, speaking of Cephalotaxus, says that this form, by "the

simple condition of its microsporophyll, which, instead of bearing numerous sporangia, has but two or three, is clearly shown to be more primitive than

Torreya or Taxus." Coomwenting further, when dealing with the relations

of Cephalotaxus to the Podocarps, he says, in connecfion with the occurrence

in that gen-us of two ovules to a bract instead of one:-'"It seems very

probable that the multiplication of sporangia, which is so evident in the male cone of the Taxineae, may have affected the female strobilus also."

These opinions have been thus fully quoted because the introduction into discussions on the antiquity of the Conifers of the primitive nature of the

stamen lends all the greater importance to a true conception of its

morphology. If more evidence is available in favour of the Coulter-tand

hypothesis applied to the Abietineae, it will be a further weakening of the

claim of that group to superior antiquity. As notes that had been gathered

on the structure of the staminate strobilus of Larix seemed to bear directly

on this question, they are here put on record.

THE MICRO-STROBILUS OF LARIX.

As the nature of the vascular bundle to the stamen held special

interest, the facts noted can best be presented under two headings: (A) general structure, (B) vascular supply.

A.-(1) General Structure of Micro-Strobibas and Stamen. The main features here have already been described (7). For our

purposes now, it is only necessary to recall that, even in the adult stage,

the stamen of Larix bears a distinct knob-like lamina, in which two

cavities are found, which are sometimes reduced to one by fusion., These

cavities are filled with resin, as treatment with copper acetate showed.

P1. XA, which is diagrammatic, suffices to bring out that the ca-vities are

strictly confined to the knob-line lamina. Vertical resin canals run in

the cone axis, b-at never approach even the base of the stamen, so that

the "apical" cavities are completely cut off from the cone axis by the

whole length of the stamen itself. Such cavities are absent in Cedrus

and Abies, as far as species are available; but are present, though poorly

developed, in Picma and Pinus. In Pseudotsuga, however, they are as

well developed as in Larix, an interesting point, in view of their affinity.

Pseudotsuga, however, differs in the complete absence of canals in the

cone axis. This fact is deemed of importance. In the bud condition of

the strobilus the cavities in the tip of the stamen are even more obvious,

as shown in P1. XB, a transverse section of the bud of Larix. Now, it

is a peculiar fact that in the vegetative bud of Larix, a transverse section

shows the paired calnals of the leaf already fully developed. These, too,

are not joined in the cortical canals of the stem, though, naturally,

they run almost the whole length of the leaf. On the assumption that



158 Proceedings of the Royal Irish Academy.

the stamen is of a true leaf-like nature, it is at once tempting to interpret the apical cavities of the stamen as the true homologues of the paired canals of the leaf, and to interpret, in that sense, paired resin cavities, wherever they may appear i-n the stamens of the Abietineae, even in Pinus laricio, as described by Coulter and Land. But the situation is

not so simple. If we examine the stamen of Cedrus, we find a condition which appears unique for that genus, as far as the Abietiueae are con cerned. It is definitely absent in Pinus, Picea, Larix, Pseudotsuga,

Abies, and Pseudotarix. Tsuga and Ketebeeria were not available. The condition is shown in P1. Xc (a longitudinal section of a stamen of

CJdrus deodara attached to its axis). Here the apical lamsina is thin,

flat, and hard, with no such cavity as is characteristic of Larix and the

other Pineae. But branches from the resin canals, which are very

numerous in the cone axis, run out as figured along the whole length

of the microsporangium. There are here, also, two such canals-one over each pollen sac. In view of the facts, then, that, in the Larch, the

apical cavities are confined to the knob and the axial canals to the axis,

that in the Douglas fir the apical ones are as in the Larch, while the

axis is free from canals altogether; while in the Cedars, the lamina is

free from resin cavities, while the axis canals run out along the stamen, it would appear that the apieal cavities of the Larch and Douglas fir

are of a different nature from the long canals of the Cedar. It is

possible, then, that in the Larch, we find quite well and constantly

developed, in addition to the normal, two rudimentary sporangia, merely

represented now by the resin cavities in the adult, a suggestion which

finds further support in the common fusion of these two cavities, just as

the abortive sporangia of Torreya connonly fuse (see P1. Xi3). The resin

canals of Cedrus never fuse.

This claim is also supported by an examination of the development of the staminate bud of Larix, which presents certain features of interest.

In the first place, the development of these apical cavities follows the now well-recognised lines. Four masses of sporogenous-like tissue are early seen, with nothing to distinguish them except their position. Detailed examination failed to show any large primary sporogenous cell, such as is described in Torreya, in the area later destined to become

cavities. But, as even in the true sporangia, the primary cells are very

small, and not particularly distinct, it was hardly expected to find such

evidence on the site of the future cavities. When the primary tissue in

the microsporangia begins its increase, no division takes place in the other

masses, but in the group of cells a separation appears. They do not

disintegrate, as described by Miss Starr for Gtnkgo, but separate, leaving

a space, which gradually increases, till a cavity is formed, lined by the

first-formed cells, which now make a definite layer, very suggestive of

a tapetum. When the cavity is thus well formed for the first time, its



DOYLE-Notes on the Staminate Cone of Larix leptolepis. 159

wall is quite like the future wall of the true sporangium, composed of

about three layers of cells. The inner layers gradually appear crushed,

but the outer layer, the epidermis, stands out so clearly at this stage, composed as it is of large firm-walled cells, that it is the most conspicuous thing in the section when glanced at rapidly under the microscope. The true sporangial wall shows no differentiation at this stage. The wall of the cavity, however, never develops the markings characteristic of the true sporangial wall. Now, this process might have been deseribed in much greater detail, but as a further elaboration seemed to have no

direct bearing on the point at issue, it seemed better merely to summarise it rapidly. But it is clear that, as in other cases, the early stages suggest

abortive sporangia; and, further, that the cavity is not merely a sort of accidental break-down, but is a definitely organised one. Its importance

may be physiological, and not phylogenetic, but its definiteness cannot be gainsaid.

In the second place, the relative size of the cavities and of the sporangia

seems of interest. P1. XD is a longitudinal section of the young micro

strobilus of Lartx leptolepis. The section has passed through the two lower stamens, bringing out an appearance very common and charac

teristic. At this stage the stamen is peltate. Were the resin cavity

filled with developing sporogenous tissue, the section might pass for a

section of the stamen of Taxus. At this stage the procambial strand

runs entirely without prejudice between the sporangia and the cavities.

If this section is compared with P1. XE, a corresponding stage in Ginkgo,

copied from Goebel's Organography, the similarity iS Temarkable.

Compare it further with P1. XF, adapted from Coulter and Land's

drawing of the stamen of Torreya at the same stage. There can be little

doubt-pace Eames and Sinnott-that the eavities in Torreya are

abortive sporangia, so the similarity here seems in the nature of a

demonstration. Exactly similar appearances are shown in Pseudotsuga.

Indeed, in some sections the peltate appearance of the young stamens

was even more striking than the figure drawn of Laris, and might well

have replaced it. In addition, the marked epidermis of the abortive

sporangia in Pseudotsuga is also quite distinct at this stage, and swings

uninterruptedly round the true sporangia, where it is equally developed, thus making the Teaxus-like appearance very notieeable.

On the basis then of the facts just described, and of those cited in the

introdtuction, there seems good ground for the claim that the primitive

stamen in the Conifer and Ginkgo phyla was of a radically symmetrical

nature carrying many sporangia. Originally, the strobilus may have

been of the Cordaianthus type. With loss of the bracts, paralleled in

the Equisetales, the need for protection may have resulted in the turning in of the sporangia yielding the peltate type of stamen. Conditions of

space and pressure can satisfactorily explain the abortion of the adaxial



160 Proceedings of the Royal Irish Academny.

sporangia. Austrotaxus spicata, Compton (28), may be of interest in

this connection. One of the many endemic Conifers of New Caledonia;

it is possibly an old type. Its male cone is elongated, and carries bracts,

in the axils of which the Taxus-like stamens arise. Considered in relation

to Cephalotaxus it is tempting, though naturally premature, to look upon

it as the "missing link."

A.-(2) Theoretical Results.

If this be correct, certain results seem to follow. Such a stamen was

never foliar, but of the same nature as the sporangiophore of the

Equisetales, i.e., with Kidston anid Lang (16), it can be considered to

represent the reduction of a primitive branching system carrying the

sporangia, a system on which the flattened photosynthetic lamina con

dition was never impressed. We cannot properly reconstruct its history

till we know more of the microstrobili of fossil Conifers, and especially

of the older Cordaitean forms. Cordaites itself seems specialised, and

caution would advise care in basing broad homologies on the structure

of the Cordaianthus strobill alone. But if we examine the suggestion

that the primitive microstrobilus of the Coniifer phylum in its widest

sense consisted, as in Cordaianthus, of a number of bracts, with such

sporangiophoric structures more or less closely related to them, we shall

find it of great value.

In the first place, it relates the microstrobili of all the living forms

to the same general plan as a known related fossil. In the second place, it enables all the megastrobili to be homologized, not only with one another,

but with the microstrobili. The argument here can be presented only in

the roughest outline. To meet even obvious objections would be beyond

the scope of these notes. But if the suggestion outlined above seems to

harmonize even a few disputed points, all the greater value can be laid

on the suggestion itself. The micro- and megastrobili in many forms, in practically all the

Pinaceae, occupy similar positions on the plant. The terminal buds on

two dwarf shoots lying side by side on a Larch branch can burst in

spring, one into a male, the other into a female cone. It would thlen seem

possible fully to homologize the two types. But in discussions on cone

morphology such homology has seldom been drawn. Accepting the

stamen as a leaf, homologous with the bract of the female cone, would

lead, if the two cones are directly comparable, to the Eichler hypothesis

in some form, but also leads to the difficulty that the microsporangia are

carried on the lower, the megasporangia towards the upper surface of

their respective leaves. Thomson (25), for instance, has faced the difficulty and has tried to solve it in these words :-' 'The simple scale groups, the

Taxaceae and the Araucarineae have, then, their micro- and macro

sporangia on opposite sides of the leaf; and, since the homosporous forms



DUYLE-Notes on the Staminate Cone oa Larix leptolepis. 161

from which the conifers were derived, the pteropsid series,. . . have their sporangia usually on the lower surface, the ovule has probably been

transferred to the upper surface in the course of phylogeny." Such a

movement has undoubtedly occurred as a rare phenomenon in a few

specialized and rather recent living Ferns (4), but there seems no shred

of evidence that it occurred in the past in any large phylum: nor can

one indeed interpret Conifers in terms of Ferns. The difficulty then still remains. On the other hand, if we adhere to the current brachyplast theory of megastrobilus morphology it does not seem possible, accepting the stamen as a leaf, to follow any easy direct line of homology. If,

however, we accept the stamen as a reduced sporangiophoric branching system, the two fall easily into line. We can consider the primitive

megastrobilus to be just such a group of sporangiophoric structures related to a number of bracts, which, however, are here retained. If, for purposes of seed nutrition, the number of macro-sporangia or ovules on the sporangiophore axe reduced, say to one, we have precisely the female

cone of the Cordajanthus type. If the sporangiophore (ovular stalk) becomes fixed in a definte position, axillary to the bract, we have a

structure, not only homologous with the cone, Cordaianthus, and with the male cones of the living forms, but a structure, from which all

the living megastrobili can be derived, by a very simple tran

sition. Consider P1. XI. A shows one bract of such a cone carrying, in its axil, a sporangiophoric stalk terminated by one ovule of typical

Palaeozoic nature. Inversion of the ovule (B, is a hypothetical inter

mediate stage), with the consequent fusions, provides an arrangement, c, which is in no way different from the diagram of the ovule of

Podocarpus spicatus given by Sinnott [(21), fig. 2, p. 44)]. It is not claimed,

of course, that the inverted ovule is primitive for the Podocarpineae. By suppression of any or all of the ovular bundles, by varying degrees of

inversion or subsequent eversion, etc., any of his diagrams of the podocarpean structures seem capable of easy and direct relation to the

primitive scheme figured in w, and of which we seem to have an actual

example in the Palaeozoic Cordaianthus. If the Abietinean scale is con

sidered to be a modified brachyplast, in the narrow sense, which subse

quently covered the ovule to form the epimation of the Podocarps, we are

forced to derive the latter from a structure for the existence of which

there is no evidence in the Palaeozoic cones. It surely seems easier to

accept an obvious transition from a structure which we know existed.

Again, acceptance of this does not mean a direct derivation of the

Podocarps from Cordaites. It is only claimed that an easy and direct

transition exists from a type of cone of which Cordaianthuts is one variant

to the generalized podocarpean structure.

If this be agreed upon, the rest follows easily. As a result of the

work of Eames (9), Sinnott (21), and others on the vascular anatomy of



162 Proceedings of the ogtal Irish Academy.

Conifer cones, it now seems hard to deny that all the types of Conifer cones are homologous, whether they be all simple or all compound being a separate question. Followers both of the simple scale theory and the brachyplast theory are now largely agreed on that point. The ovuliferous scale of the Abietineae and the ovular stalk epimatium of the Podocarps are homologous structures, the condition in the Araucariae, Taxo dineae, &c., falling into line as less developed or more reduced variations of the same plan. In other words, all the megastrobili can be, therefore, related to the type diagrammatized in P1. XI. In the Taxaceae, the outer

integument may later develop fleshy in relation to spread by birds; and, just as in the angiosperms we have the numerous dry fruits as well as

the succulent ones, so here in the Pinaceae, in relation to the protection

of numerous seeds, a dry hard cone is formed. Here the axillary scale,

fused or free, may be the opening out of the epimatium, which is practically Celakovsky's view, or an outgrowth and expansion of the ovular stalk, there being no means yet of deciding which. All the cone types may have

had an independent origin. If we so fancy, we may consider the

Araucarian type, for example, derived by an early fusion of bract and

ovule in c (ef. Podocarpus dacrydiocdes), and a lack of development of the epimatium and stalk parts. And so with the other groups.

Since, then, the conception of the Conifer stamen as definitely non foliar, but of a sporangiophoric nature, in the sense outlined above, can

be used to homologize the megastrobilus and the microstrobilus, deriving both from a primitive Cordaianthus-like type, there seems a strong

theoretical argument in favour of an hypothesis based on observed

anatomical facts. Finally, if this be correct, two arguments in favour of Jeffrey's theory

of the superior antiquity of the Abietineae over all other Conifer groups

are weakened. The first, namiely, that two is the primitive number of

pollen sacs in the Conifers, and that the Abietineae are, therefore,

primitive in this regard, would go by the board. The second deals with

the brachyplast conception. Jeffrey's theory would almost seem to stand

or fall with the brachyplast theory of cone morphology, interpreting

brachyplast in the narrowest sense as a dwarf shoot, like the dwarf shoot

of Pinus (13). Not only are the Abietineae deemed the oldest group, but

Pinus itself is deemed the oldest Abietinean form, largely because it shows

in its vegetative structure the brachyplast arrangement, which, it is

claimed, is fundamental in the structure of the conservative reproductive

organ, the megastrobilus. Now, there is no scope in these notes for an

adequate treatment of the brachyplast. But, on the hypothesis just

stated, while admitting the branch nature of the axillary structures in

the female cones, there is dropped completely the ideai of its ever having

passed through the stage of a vegetative- shoot, in the narrow sense, dwarf

or long. In that sense there is no fundamental brachyplast unit in



DOYLE-Notes on the Staminate Cone of Lar&x leptolepis. 163

Conifer morphology. The structure is the modified development from the primitive branching system, wholly given over to reproduction since its earliest appearance in the dim pre-Devonian past among some group

of Rhynie-fossil-like. ancestort

B.-TJt Vascular Bundle of the Stamen.

1. The single bundle runs out, as usual, over, and medianly to, the

pollen sacs. As it passes out it becomes accompanied by transfusion-like tracheides, to be dealt with later, which become more and more numerous

as it approaches the distal end of the sacs. Here it expands into a broad

horizontal bar, sends down a small wedge, almost entirely composed of the

short transfusion-like elements; then, dividing, sweeps into two masses of similar tissue up to the resin cavities of the apical knob, with which they

come into fairly close contact over a large area. This general course

emphasises the importance of these resin cavities. It would almost appear

as if the vascular connection with the old sporangia had been retained

and modified in connection with some physiological function now played in the nourishing of the spores by the replacing resin masses. No

physiological explanation of the peculiar course and development of the bundle can be offered.

2. A point on the thickening of the vessels needs noticing. On the

transitional vessels, between the proto- and later-formed xylem, sometimes even on the latter, and sometimes even on the transitional elements

between the ordinary elongated vessels and the transfusion tracheides, bordered pits and spiral, annular and band thickenings occur on the same

tracheide. Now, this condition is almost certainly merely what it appears

to be-the overlapping on the small, poorly-dtveloped vessels of the two

types of thickening. But as similar markings have been used in phylo

genetic discussions it needs remark. Dupler (8) describes the xylem of the staminate strobilus of Taxus canadensis as consisting of spirally

thickened tracheides with bordered pits. He does not say if he considers

this of the same nature as the markings on the tracheide walls of the adult

stem. It is, however, well to note that it is definitely not so. The

typical Taxinean spirals are tertiary spirals; these are in the secondary

wall only. Again, the claim for, the relationship of Phyllocladus with

the Taxineae rather than with the Podocarpineae has been supported (19)

by reference to the appearance in normal primary xylem as well as in

transfusion tracheides in the cladodes of Phyllocladus of a combination of

bordered pits and band-like thickenings. Sahni (20) points to the

existence of the same type of thickening in the primary xylem of

Aemopyle, two species of Podocarpus, ancd one of Dacrydium. He does

not say what value he places upon it. Its common occurrence, however,

in young male cones seems to make any such phylogenetic importance

very doubtful. It occurs not only in the cones of Larix, but in cones



164 Proceedings of the lRoyal Irish Academy.

of Picea, Pseudotsuga, and Gimkgo; and in Prepinus leaves (14). Of course, in Larix, Picea, Pseudotsuga tertiary spirals are fundamental in

the wood anatomy (1); but, as mentioned above, the bands and spirals in

these examples of primary wood are not a tertiary phenomenon at all.

The point may possibly, but doubtfully, be worth fuller investigation. 3. The transfusion tissue.-In the axis of the mierostrobilus we find

a close ring of ordinary small endarch, collateral bundles, one of which is

drawn in PI. XIIA. They call for no special remark. The bundle to the

stamen remains just like this for some way out along the stalk, but as it

approaches the area of the pollen sacs it increases in size, usually

laterally, as indicated in P1. XIHB. Here the large outer elements would

undoubtedly be inieluded as "'transfusion" tissue, consisting as they do

of wide-lumened tracheides, short in length. But examination of almost any bundle shows that the grade from these inwards to the typical, long,

narrow vessels of the normal xylem is absolutely graduial, Indeed, the greater the bundle expansion the more gradual the grade is. This grade

is not merely in length and lumen, but also in marking. The transitional

elements are commonly marked with the combination of bands and pits.

The outermost wide trabheides are most commonly banded, but, eVen in these, the combination of marking so common in the ordinary vessels is often found. The grade, too, is a physical one-meaning thereby, that there is very rarely any discontinuity in the relation of any of the vessels.

Only rarely is the condition seen on the left of PL. XJlc found, where

some of the transfusion elements are separated by a narrow line of

parenchyma from the rest of the xylem. This bundle, however, shows

the appearance, which is quite common, of elements ventral to thle

protoxylem. Elements in this position are more commonly of a transitional type, more seldom typical transfusion elements. As the

bundle passes out over the pollen sacs the condition foreshadowed in

PI. XHIc becomes common and definite. At this stage most of the bundles

show the condition of P1. XIID, where a definite mesarch state is arrived

at. Here we have a case where the true centripetal elements are quite

continuous, by gradual grade of shape, with the transfusion elements.

Finally, towards the distal end of the pollen sacs, we find regularly the

type of vascular formation shown in PI. XIIE. In the hurry and interest

of the examination of these, it was not till the xylem was almost com

pletely outlined in the camera lucida that it was realised that the phloem

was torn and imperfect. As the xylem part, however, was rather good, it

was decided to finish it as it stood. A word of explanation is necessary

here. At first glance the transfusion elements here seem of enormous

size at the edges of the bundle. This is due to the line of section, which

went through the area where the bundle was beginning to send down

the wedge-shaped continuation towards the pollen sacs, as earlier described. Thus, all the larger elements have really been cut partly in longitudinal



DOYLE -Notes on the Staminate Cone of Larix leptolepis. 165

section. The element marked t is about the largest of the elements cut in accurate cross-section. The protoxylem can be detected in the centre. In longitudinal sections of such a bundle it becomes really impossible to say where true xylem ends and true transfusion tissue begins. Elements, say, in the position X' cannot be distinguished in shape from the larger elements of the normal centrifugal xylem. Thus, leaving to one side for a moment the true wide, short elements of transfusion tissue, it is clearly seen that, often early in its course (P1. XIIH), almost always towards its termination, the bundle of the stamen becomes definitely mesarch. This condition has been described by Dupler (8) for the bundle of the staminal stalk of Taxus canadensis, but with the interesting difference that in Taxus, transfusion tissue is completely absent. [To the writer's great regret, an article by Bernard (2), which may be of speeial interest in this connection, was inaccessible at the time. From a short summary, however, in the Botanisches Centralblatt, the paper seems to deal with female cones only.]

The interest in this bundle lies not so much in its mesarch nature, as it is only to be expected that examination of a number of conservative organs like staminate strobili would be likely to show it, but in its bearing on the question of the nature of transfusion tissue. A considerable literature has gathered round this question; especially, indeed almost exclusively, concerning itself with transfusion tissue in leaves.

Worsdell (27), and more recently Miss Carter (5), have summarised all the important older papers. It is now well known that to Worsdell the transfusion tissue of Gymnosperm leaves is a special modification of the primitive centripetal xylem. Bernard (3) (in another inaccessible article) is of the same opinion. Jeffrey's (12) suggestion of an indirect origin from centripetal xylem through the inner bundle sheath of Cordaites principatis-itself a derivative of the centripetal xylem-the true centri petal xylem, as xylem, having been completely lost, is adequately dealt with by Thomson (26), who is also in favour of the Worsdell suggestion Worsdell bases his view on the following facts :-(a) The ocecurrence in

the cotyledonary bundles of Ginfgo and Cycas revotuta of an intimate union, and gradual transition between the tracheides of the centripetal xylem and those of the transfusion tissue. (b) In other Conifers, where centripetal xylem fails, the centripetal nat;ure of the transfusion tissue is shown by its frequent presence on the ventral side of the protoxylem, by the frequent extension of laterally placed transfusion tissue to the ventral side, and by the transitions in structure already named. But this view is not unanimously held. Among,others, it has been combatea

recently by Miss Carter (5) and Takeda (24). The latter article is largely

a claim in favour of the water-storing function of the tissue, but supports

Miss Carter, who objects to the centripetal nature of transfusion tissue

on the grounds that in a study of many cotyledons the following resultI



166 Proceedings of the Royal Irish Academy.

seem clear:-nIf little developed, it is lateral, not adaxial: if well

developed, it begins laterally, and is not more abundant on the adaxial

side: only in Sciadopitys is it greatest at the tip: and, finally, to quote, "if it appears in the adaxial position, it never abuts directly on the xylem

of the bundle. It is always separated by at least one layer of parenchyma.

This seems a point of importance in view of the transition emphasised by Worsdell." The transfusion tissue, then, from this view-point, does not develop centripetally, and is a modification of parenchyma only. Now, the writer must confess to complete lack of bias, and is quite open

to conviction either way, but feels that the bundle structure of the Larix stamens tells in favour of Worsdell. Thus, it is easy to make too

much capital out of the fact emphasised by Carter and Takeda-that the

transfusion tissue is usually lateral in its origin. Because, in view of its

presumably specialised functions in the leaf, it is possible that adherence to strict morphological development might interfere with that function.

Till we know the function we cannot say. And, after all, growth from

a lateral to a ventral position, in view of this, is not incapable of inter

pretation as a modified centripetal formation. While, if we examine the staminal bundle, in which presumably the specialised function of the tissue is not the same, we find, in contradiction to Miss Carter, that the

tissue may be greater on the adaxial side, may be greatest at the tip, and,

above all, we find no separation, except very rarely, between the trans

fusion tissue and the rest of the bundle. This complete continuity of all tracheidal tissue seems important, coupled as it is with an even more

complete transition in shape and size between the elements than is

described by Worsdell. Even if we were inclined to deny any mesarch

condition in the Larix stamen, and to attribute all the ventral elements

to parenchymatously originated tissue, the presence of centripetal xylem in Taxus would certainly prevent us. Figures E, c, D, B, PI. XII, in that

order, seem a series in reduction. On the whole, the vascular bundle of

the stamen of the Larch seems to demand the interpretation of a large

part, at any rate, of its transfusion tissue as being a modification of

centripetal wood. Of course, the influence of tracheide formation can

pass out beyond the limits of a primitive bundle area, and affect neigh

bouring parenchyma. Witness the layered sheet of transfusion tracheides round the microsporangium, and connected to the bundle on

the stamen of Pseudotarix (15). On the other hand, the fact recorded by Thomson (26), that, where a secondary root is given off in Agathis

Moorei, the metaxylem elements may become considerably shortened, and may completely resemble typical transfusion tissue, shows that such need

not necessarily be parenchymatous in origin.

The question still remains open, but it is abundantly clear that the

microstrobili of Conifers would well repay more intensive study than

they have heretofore received.



DoYu,r,-Notes on the Staminate Cone of Larix leptolepis. 167

SUMMARY.

1. Evidence is presented from Larix and other Conifers in support of the theory that the primitive stamen of the Conifer and Ginkgo phyla was a radically symmetrical structure, carrying numerous sporangia distally attached, and of a non-foliar sporangiophoric nature, i.e., a modification of a primitive reproductive branching system, upon which the flattened, photosynthetic lamina condition was never impressed.

2. This conception allows an easy and direct homology to be drawn

not only among the megastrobili of Conifers, but between these and the microstrobili, and between both and a primitive strobilus of the Cordaian thus type.

3. The vascular bundle of the stamen of Larix becomes mesarch distally, and develops such an arrangement of transfusion tissue as to support the claim that such tissue is itself phylogenetically a modification of centripetal xylem.

4. The micro-strobili of Conifers would well repay more intensive study.

I wish to record a deep indebtedness to Sir Frederick Moore and Mr. J. W. Besant, of the Royal Botanic Gardens, Glasnevin, Dublin, for

permission to gather cones from many trees; to Miss Agnes Murphy, M.Sc., to whose skill many of the drawings are due, and to my wife for the

others.

LITERATURE CITED.

1. Bailey, L?The Structure of the Wood of the Pineae. Bot. Gas., vol. xlviii, 1909.

2. Bernard, Ch.?Le Bois centrip?te dans les Feuilles des Conif?res.

Beiheft z. botan. Centralb., vol. xvii, 1904.

3. Bernard, Ch.?Le Bois centrip?te dans les Bract?es et dans les ?cailles

des Conif?res. Ibid., vol. xxii, 1907.

4. Bower, F. O.?The Filica?es. Cambridge Univ. Press, 1924.

5. Carter, Miss M.?A Reconsideration of the Origin of Transfusion

Tissue. Ann. Bot., vol. xxv, 1911.

6. Coulter, J. M. and Land, W. J. G ? Gametophytes and Embryo of

Torreya taxifolia. Bot. Gaz., vol. xxxix, 1905.

7. Doyle, J.?Observations on the Morphology of Larix leptolepis. Proc.

Roy. Dub. Soc, vol. xi, 1918.

8. Dupler, A. W.?Staminate Strobilus of Taxus canadensis. Bot. Gaz., vol. Ixviii, 1919.

9. Eames, A. J.?The Morphology of Agathis australis. Ann. Bot., vol. xxvii, 1913.



168 Proceedings of the Royal Irish A cademy.

10. Hutchinson, J.?Contributions towards a phylogenetic Classification of Flowering Plants. Pt. 3. Kew Bull., 2, 1924.

11. Jeffrey, E. C.?The comparative Anatomy and Phylogeny of the

Coniferales. Pt. 2?The Abietineae. Mem. Bost Soc. Nat. Hist., vol. vi, 1905.

12. Jeffrey, E. C.?On the Structure of the Leaf in Cretaceous Pines.

Ann. Bot, vol. xxii, 1908.

13. Jeffrey, E. C.?The History, comparative Anatomy and Evolution

of the Araucarioxylon Type. Proc. Amer. Acad. Arts. Sei., vol.

xlviii, 1912-13.

14. Jeffrey, E. C.?Anatomy of Woody Plants. Chicago, 1917.

15. Jeffrey, E. C. and Torrey, R. E.?Ginkgo- and the microsporangial Mechanism of the Seed Plants. Bot. Qaz., vol. lxii, 1916.

16. Kidston and Lang.?On Old Red Sandstone Plants showing Structure.

Trans. Roy. Soc, Edin., 1921.

17. Lawson, A. A?The Gametophytes and Embryo of Pseudotsuga

Douglasii. Ann. Bot, vol. xxiii, 1909.

18. Eobertson, Agnes.?Spore Formation in Tor rey a calif or nica. New

Phyt, vol. iii, 1904.

19. Eobertson, Agnes.?Some Points in the Morphology of Phyllocladus. Ann. Bot., vol. xx, 1906.

20. Sahni, B.?On the Structure and Affinities of Acmopyle Pmcheri,

Pilger. Phil. Trans. Roy. Soc, B. 210, 1920-21.

21. Sinnott, E. W.?The Morphology of the Reproductive Structures in

the Podocarpineae. Ann. Bot., vol. xxvii, 1913.

22. Starr, Anna M.?The Microsporophylls of Ginkgo. Bot. Gaz., vol. xlix, 1910.

23. Stopes, Marie C.?Catalogue of the Mesozoie Plants in the British

Museum. Pt. 2, 1915.

24. Takeda, H.?A Theory of Transfusion Tissue. Ann. Bot, vol. xxvii, 1913.

25. Thomson, R. B.?The Megasporophyll of Saxegothaea and Microcachrys.

Bot. Gaz., vol. xlvii, 1909.

26. Thomson, R. B.?On the comparative Anatomy and Affinities of the

Araucarineae. Phil. Trans. Roy. Soc, B 204, 1914.

27. Worsdell, W. C.?On Transfusion Tissu'e. Its Origin and Function

in the Leaves of Gymnospermous Plants. Trans. Linn. Soc. Bot.,

2nd ser., vol. v, 1895-1901.

28. Compton, R. H.?A systematic Account of the Plants collected in

New Caledonia arid the Isle of Pines in 1914. Pt. 2. Journ,

Linn Soc? Bot, vol. xlv? 304, 1922,



soc. RI.A., VOL. XXXVII, SECT. B. PLATE X.

~~QKJ

DOYe.-THE STAMINATE CONE OF LARIX LEPTOLEPIS.



PRoc. R.I.A., VOL. XXXVII, SECT. B. PLATE XL

S~~~~~~~~~~~~~~~~ 1

DOYLE,-THE STAMINATE CONE OF LARI:i LEPTOLEPIS.

DoYnm.-THE, STAMINATE, CONE OF LARIX LJEPTOLEPIS.



PRoc. R.I.A., VOL. XXXVII, SECT. B. PLATE XII.

DOYLE.-THE STAMINATE CONE OF LAIX LEPTOLEPIS.



DoymLE-Notes on the Staminate Cone of Larix Leptolepis. 169

EXPLANATION OF PLATES.

PLATE X.

A.-Diagrammatic L.S. of stamen of Larix, to show relation of pedicel resin canal and the cavities in the lamina or "apical knob."

B.-T.S. staminate bud of Larix, showing fusion of the cavities in the "knob." X 75.

C.-Diagrammatic L.S. of stamen of Cedrus deodara, to show pedicel resin

canal running out over microsporangium, and no cavity in the

lamina. X 17.

D.-L.S. young microstrobilus of Larix, showing peltate form of young stamens. X 75.

E.-L.S. young microstrobilus of Ginkgo for comparison with D and F

(from Goebel's Organography).

F.-L.S. young stamen of Torreya for comparison with D and E (from Coulter and Land).

PLATE XI.

Diagram to show relation between a primitive strobilus arrangement of the Palaeozoic and the podocarpean type of ovular attachment. [Explanation in text.]

PLATE XII.

Vascular bundles from the microstrobilus of Larix, all X 600.

A.--Showing the normal type in the pedicel.

B, C, D.-Type occurring about half out along the stamen, showing the transfusion tissue (larger xylem elements), continuous with and grading into the ordinary xylem. In D the protoxylem is definitely mesarch.

E -Type occurring well out along the stamen, showing large development of "'mesarch transfusion" tissue.

PfLOC. R.i.A.7 VOL. XXXVII, SECT. ii, 12 C]



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Notes on the Staminate Cone of "Larix leptolepis"