144 SYDNEY H. VINES.

crackling noise. The fasciculi of the first order are dis-tinguished by their aspect as well as by the great resistance theyoffer to the probe, which may need to be aided by a few strokesof a knife. The fasciculi of the second order are distinguish-able by their fineness and the readiness with which they break.They may be further recognised on membranous layers whichhave been entirely detached, and which, though apparentlysmooth, give to the finger when lightly passed over the surfacethe sensation of numberless points so closely set together as tofeel like a fine brush. Moreover, when viewed with a magnify-ing power of 40 diameters, they are seen to be perpendicular tothe surface of the detached layer, whereas the broken ends of thefirst order of fasciculi are not only larger, but lie flat on thefibrous layer.

I cannot doubt, that the objects here described are really theperforating fibres; at the same time, I cannot well conceive thatthose I have met with, small and soft as they are, should feelunder the finger like the hairs of a brush, however fine.

Respecting Dr. dementi's note, I have further only to pointout that he is in error when he asserts, as he does (p. 12), thatI did not notice the existence of the, fibres in question in flat ortabular bones; and, in conclusion, I cannot help saying thatwhen I first observed these fibres I had no idea that they badbeen recognized before, still less did I imagine that the subject ofmy observation would ever acquire such importance as to lead toa formal claim of priority on the part of Italian science.—Yoursfaithfully, W. SHABEEY.

E. A. Schafer, Esq.,Dec. 1, 1877.

RECENT RESEARCHES into the NATURE of LICHENS. By SYDNEYH. VINES, B.A., B.Sc, Fellow and Lecturer of Christ's College,Cambridge.

IN previous volumes of this Journal,1 Mr. Archer has tracedthe history of the discussion upon Schwendener's theory from itscommencement in 1868 down to the end of the year 1873. Iwill endeavour to maintain the continuity by briefly alluding tothe principal papers which have appeared upon the subject duringthe intervening years, reserving the more recent publications fora somewhat detailed account.

1 Vols. xiii and xiv.

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 1 4 5

The last paper mentioned by Mr. Archer in his resume* is theimportant one by Treub,1 published in November 1873. In the' Flora' for January 1874, J. Muller hastens to combat theresults at which Treub had arrived. He regards the question asstill an open one, in spite of the recent publications of Treub andBornet, and maintains firmly the accuracy of his own observa-tions in which he distinctly traced the development of thegonidium from the hypha in Synalissa Saleoensis. He goes sofar as to say that, even if his own observations were inaccurate,the new theory cannot be considered as established until it isascertained that the spermatia give rise to hyphoid and not togonidial products. Miiller's paper was soon followed by anotheron the same side from the pen of Nylander.2 In it are repeatedmost of the objections which this distinguished lichenologist hadalready raised to the acceptance of Schwendener's theory, andattention is particularly drawn to the fact that those Algse whichare regarded by the supporters of the theory as playing the partof gouidia in various Lichens—such Algee, for instance, as Cora,Dichonema, Scytonetna, Sirosiphon—are held by him to be them-selves of the nature of Lichens. From this point of view,the new theory of the structure of the lichen-thallus is simplyabsurd.

In the July Number of the ' Popular Science Review/ of thesame year, the Rev. J. M. Crombie, comes forward as anotheropponent of the new doctrine. In his article he gives a briefhistory of the whole discussion, and sums up strongly in favourof the older views. He is especially severe upon one of Bornet's" strong points," viz., the identity of Protococcus viridis withthe gonidia of Physcia parietina. He admits the similarity ex-istingl between these organisms, but cannot recognise it asamounting to identity, for the gonidia of Physcia are larger andmultiply less actively, while Protococcus multiplies very rapidly.Some facts, to which attention will subsequently be called, willshew that these differences of habit do not suffice to prove theseorganisms to be distinct.

Later on in the year an elaborate defence of the older viewswas published by Korber.8 He lays down three propositions,(1) that the tissue in which the gonidia of a Lichen are em-bedded is not of a fungoid nature; (SJ) that the gonidia are nottrue AlgEej and (3) that Lichens are not the expressions of acondition of parasitism. In support of his first proposition herecalls the differences which Von Krempelhuber pointed out asexisting between the tissues of Lichens and those of Fungi, but

1 ' Onderzoek. over de Natuur der Lichenen. Leiden.'3 'Flora/ abstracted by the Rev. J. M. Crombie in 'Grevillea,' vol. ii.3 'Zur Abwehr der Schwendener-Bornet'scben Elechtentheorie/ Breslau.

1 4 6 SYDNEY H. VINES.

admits that these differences do not hold good in all cases. Hestates as a fact that there are Lichens, for the most part crusta-ceous, such as Secologia ahstrusa, Hymenelia affinis, Sarcogyneprivigna and others, which have no hyphse in their thallus,although asci and paraphyses are present. Such a fact as thishe considers to be a crushing proof of the absurdity of Schwen-dener's theory, for here are Lichens in which only one of thevisual constituents is present.

In support of his second proposition he points out thatBaranetzky has observed the protrusion of hyphal filaments fromgonidia, and adds that he has himself seen this occur in Poro-cyphus and Collema. Such an occurrence is quite unknownamong the true Algse. Furthermore, it is well known thatseveral forms of gonidia may occur in the same lichen-thallus, asin Harpidum rutilans, Pannaria granatina, Hacoblenna irem-niaca, &c, and Korber suggests that it is extraordinary that aLichen should require so many forms of Algee to act as thegonidia of its thallus. He concludes his argument by sayingthat if the gonidia were true Algse they would by this time,have been all met with in the free state, whereas this is by nomeans the case; the gonidia of Nsetrocyinbe, Phylliscum,Melanormia and others, for instance, have not yet been foundelsewhere than in the lichen-thallus. Moreover, he insists thatwhen gonidia are found in the free state, they are not thereforeto be regarded as Algse. Finally, he lays stress upon the apparent-fact that the gonidia resemble only such so-called Algse as repro-duce themselves solely by division.

In supporting the third proposition, the author adopts theview of Fries, according to which the term " parasitism" is inap-plicable in describing the connection of the " fungus" with the" alga" in a lichen-thallus, and adds that if any " parasitism"exists at all it must be mutual, pointing out that in a thallusthere are so many gonidia which are not connected with hyphsethat the relation of the latter to the former must be other thanthat of a parasite.

In the concluding paragraphs he recalls, as Miiller also doesin his above-mentioned paper, the old view of the origin of thegonidia from the hyphse, and goes on to say that if the connec-tion of the gonidia with the hyphse is not of a genetic nature, itmust indicate some nutritive process by which the gonidiumobtains from the hypha some of the material which is essentialto its existence. From this stand point he ventures upon someremarkable speculations as to the probable details of this nutri-tive process which need not be considered here.

He enumerates finally the various modes in which a lichen-thallus may be reproduced, six in all, of which two are by means

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 147

of spores,1 and four by gonidia with (soredia) or without hyphse.The fact that a lichen-thallus may be developed from cells whichdo, as well as from cells which do not, contain chlorophyll estab-lishes, he considers, the autonomy of the Lichens.

Of the publications which afford evidence in favour of Sch-wendener's theory the first is that of Borzi.2 In it an accountis given of numerous " culture" experiments made with variousLichens, such as Parmelia puherulenta, Physcia ciliaris, andothers. The conclusions to which the observations led were thefollowing: (1) that the gonidia stand in no genetic relation tothe hyphffi, but that on the contrary they are autonomousorganisms, true Algse, which serve as hosts for the hyphse;{%) that the relation between the hyphse and the gonidia is alwayssuch as exists between a Fungus and the substratum upon whichit lives; and (3) that Lichens consist of ascomycetous Fungiparasitic upon their gonidia, which are true Algse.

An important contribution to the discussion is the paper byBornet.3 He begins by giving some account of cases observedby him in which the gonidia of certain Lichens reassumed theiralgal condition. In certain old thalli of OpegrapM varia—thegonidia of which are furnished by filaments of Trentepohlia(Chroolepus)—he found that the gonidia had here and thereregained their normal structure. They had become elongatedand had produced numerous sporangia, such as are peculiar tothe genus Trentepohlia, and numerous zoospores could be de-tected moving amongst them- These fertile filaments were dis-tinctly continuous with those which were still acting as thegonidia of the Lichen. Again in Pannaria triptophylla, Nyl.var. nigra, he frequently found projecting from the tubercles ofthe tballus which had become ruptured, filaments which wereevidently prolongations of the mass of bluish gonidia containedin the thallus of this species. These observations convinced himthat the two kinds of gonidia in the thallus of this Lichen,though so different in appearance, are really two forms of thesame Alga. The filamentous gonidia are but slightly modifiedforms, but in the spherical gonidia the original normal algal formis no longer recognisable.

Further, the thallus of Collema, as is well known, becomescovered under certain circumstances with great numbers ofsmall round grains, produced from the extension and developmenttowards the exterior of a fold of the gonidial filaments. Usually

1 He states that he has observed in Sphserornphale the direct development of gonidia from spores (?).

3 'Intorno agli oilici dei gonidi de'Liclieni, Estr. dalla Scienza con tern-poranea, Palermo.' Reprinted in ' Nuov. Qiorn. bot. Ital.,' 1875.

3 "Deuxieme note sur les gonidies des Lichens," 'Ann. Sci. Nat.,' ser.v, t. x.ix.

148 SYDNEY H. VINES.

hyphae penetrate into this excrescence as it forms, and the resultis that these microscopic grains possess the two structural ele-ments of a Lichen. It occasionally happens, however, as DeBary1 has shown, that they have no hypbse. They are then simplyNostocs which entirely resemble those which are to be foundamongst Mosses. Nearly always in such cases the young Nostocwhich is attached to the Collema only by a slight gelatinouspedicle, becomes detached.

He goes on to cite other examples of the same kind with theview of proving that the gonidia can easily take on the charac-ters of free Algse and vice-versa. He concludes this part of hispaper by referring to the genus Lichina, expressing an opinionthat the gonidia of this genus are formed by filaments of someRivularia, an opinion which was fully borne out by Kny's re-searches upon the development of the thallus of Lichina p-ygmea?which were published later in the year.

Having brought so much evidence to prove the identity of thegonidia of many Lichens with certain of the lower Algae, hegoes on to discuss objections which might be raised against thisview, such an objection, for instance, as that raised by Korber(see ante), that these Algae are not autonomous organisms butsimply the gonidia of Lichens in a free state. Such an hypo-thesis, he says, is quite inconsistent with our present know-ledge of Algae, for it is certain that these same Algae do notmultiply merely by division, but also by a fructification of theirown which is quite distinct from that of the Lichen. He thenbriefly gives an account of various investigations which have beenmade into the life-histories of the gonidia, such as Famintziuand Baranetzky's discovery of zoospores in the Cystococcushumicola extracted from the thallus of various species of Lichens,his own observations of the emission of zoospores by Trentepohliawhich furnishes the gonidia of Opegrapha varia, and draws at-tention to the similarity, amounting to identity according toPringsheim, of Phyllactidium which furnishes the gonidialelement of Opegrapka fiUcina, with Cceleochsete.8 Here thenare numerous instances of the multiplication of gonidia by cer-tain specialised reproductive processes, and many instances of thekind may be cited as occurring amongst those gonidia whichbelong to the Phycocbromacse.

He concludes by recounting his experience of separate cul-tures of gonidia, and of spores of Lichens. The former multi-plied immensely but no trace of a hypha could be detected—thelatter germinated and grew, but no gonidia were developed.

1 ' Handb. d. Phjs. Bot.,' Bd. ii, Abth. i, p. 290.3 ' Sitzber. d. gesellsch. naturf Freunde in Berlin,' Nov., 1874.8 See tbis Journal, vol. xv, p. 334.

RECENT RESEARCHES INTO THE NATURE OF LICHENS. J 4 9

In the 'Counptes Rendus ' for November, 1874, H. A. Wed-dell draws attention to the Lichinese as being very favorableobjects for observations of this kind. The gonidia not onlyform the greater part of the thallus of the Lichens, but theyregulate its form. The hyphse lie in the gelatinous investmentand bear the apothecia. Such Lichens have been termed pseudo-algae. Unfortunately this term has been extended to thoseAlgae which the opponents of Schwendener's theory regard asimperfect Lichens, that is, as gonidia; such are Stigoneraa andScytonema. If it can be proved that there are true Algse, oneof the strongest objections to the theory would be overthrown.He considers that such evidence has now been collected. Theresearches of Janczewski, and of Thuret and Bornet, upon thereproduction of Nostoc by spores demolish the argument that itis an imperfect or a modified form of Collema; and the re-searches of Bornet (see ante) upon the gonidia of Opegraphahave the same effect. He then brings forward a communicationmade by Gibelli to the Botanical Congress held at Florence(May, 1874).1 Gibelli had observed the formation of zoosporesin the gonidia of Leeanora subfusca while still in the thallus.This observation Weddell says enables us to account for the so-called spontaneous appearance of gonidia in parts of the thalluswhere none had previously existed. Gibelli also confirms Bornet'sexperiments on Opegrapha.

At a meeting of the Societe* Botanique de France, held onNovember 27th, the physiological aspects of the question werediscussed. M. Cornu opened the subject by saying that thepeculiar parasitism exhibited by Lichens was not sufficient groundfor separating them from other Ascomycetes. Such a parasitismexists also in other families of the same group, as, for example,that of Spharia cupularis upon the red stroma of Nectriaeinnabarina, and again, of Asterosporium Hoffmanni upon Cucur-bitaria macrospora. M. Weddell pointed out that in theseexamples the two organisms belonged to the same family groupof plants, whereas in Lichens it was a cohabitation of organismsbelonging to different classes. The term "parasitism" if usedto describe this cohabitation is used in a forced sense, for the hostinstead of suffering grows the more vigorously.

M. Cornuj in reply, referred to the observations of Bornet,from which it appears that the form of the Algae is somewhatmodified under the influence of thehyphae. M. Weddell rejoinedthat in Collema and its allies the hyphae do not come into contactwith the cells of the Nostoc filament, and that, moreover, themodification of the Alga in other Collemaceae under the influenceof the hyphae is not such as could forbid the assumption that the

• l ' Atti del. cong. intern, bot. Mrenze 1876.'

150 SYDNEY H. VINES.

vegetation of the Alga is under these circumstances more active.M. van Tieghem distinguished two kinds of parasitism ainougFungi, (1) necessary and (2) voluntary, examples of which lieadduced in illustration. In Lichens it is otherwise, the cohabi-tation of Alga and Fungus is a reciprocal parasitism, the Algaprobably supplying the Fungus with carbohydrates and being, inreturn, preserved from desiccation by the investing hypbee.

To the number of this Journal for January, 1875, Archercontributed a paper "On Apothecia in some Scytonematous andSirosiphonaoeous Algae in Addition to those Previously Known."His researches were suggested by those which led Bornet1 toremove Stigonema atrovirens from the Algse and to place itamong the Lichens under the name of Ephebe pubescent; andtheir object was to discover, if possible, in allied forms the dis-tinctly lichenous fructification—apothecia and spermogonia—•which this species of Stigonema had been found to possess.Archer was successful in discovering apothecia in Scj/tonemamyochrous, as well as in another unidentified form, in two speciesof Svrosiphon {alpinus and pulvinatus), and finally in Stigonemainamittoswn. He was, therefore, led to assume that these generaand probably the whole of the Scytonemacese and Sirosiphonacesecould be no longer properly accounted Algse, but should berelegated with Ephebe to the Lichens. Archer was unable todetect any hyphse in the species which he examined, thoughSchwendener had found them in Ephebe and Bornet in Spilonmaparadoxum and in JJichenosphmria Lenormandi, nor could hediscover any spermogonia.

The next important publication is that of Arcangeli.1 In thegeneral discussion of the question which precedes the account ofhis own researches, he points out that Schwendener's theory hasin its favour the fact that Fungi are parasitic plants incapable offorming chlorophyll so far as our present knowledge extends.He argues that it is not, however, impossible to imagine theexistence of plants which, though of a distinctly fungoid nature,may yet be able to form chlorophyll and to assimilate. Lichensundoubtedly resemble Fungi very closely both in their vegetativestructure and in their reproductive organs, why then, he asks,may not Lichens be regarded as plants belonging indeed to thegroup of Fungi but containing chlorophyll? In the Phanero-gams examples occur of natural families, some members of whichdo, and some do not, contain chlorophyll.

He brings forward some observations in support of this viewwhich tend to prove that chlorophyll may occur in cells of Lichens

1 "Recherches sur la structure de l'Ephebe Pubescens," 'Ann. Sci.Nat,' s6r. iii, t. xviii.

3 ' Sulla questions dei gonidi, Nuov. Giorn. hot. Ttal., 1875.

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 1 5 1

other than their gonidia. For instance, he believes that he haadetected grains of phycochrome in the spores of some Colleineseand Parmelieae, and a green substance in thehyphse of the thallusof Pannaria triptophylla.

He regards the researches of Janczewski, of Thuret, and ofBornet, which give us a knowledge of the complete life-cycle ofNostoc as affording strong evidence in favour of Schwendener'atheory, but he does not consider that it suffices to prove theautonomy of Nostoc. The well-known heteroecious mode oflife of Fungi, as well as their polymorphism, render it quiteprobable that such phenomena should also be observed in agroup so nearly allied to them as that of the Lichens.

Then follows an account of various observations of compara-tively small importance which tend to prove the similarity of thetissues of Lichens and Fungi, and of others respecting themode of connection between the hypha and the gonidia, whichhe has found, in some cases, to be different from that describedby Bornet. With reference to the development of the gonidiahe concludes from his observations upon Usnea barbala, Alectoriaiubata, and Ramalina farinacea, that in the apices of thebranchings of these Lichens gonidia are developed from thehyphse, for he found them quite isolated in such positions thattheir origin could not be referred either to a division of pre-viously existing gonidia or to the entrance of zoospores fromwithout. He detected a peculiar mode of development iuCladonia rangiferina. At the extremities of the branchings ofthe thallus he found groups of cells, with ill-defined contours,in which the hyphse became lost. Near to the apex thesecells are colourless, but farther back they are coloured green(gonidia), and between these extremes all intermediate stagesoccur. The author is inclined to regard these groups of cells asSoredia.

In many foliaceous and crustaceons Lichens, such as Nepkro-ma levigatum, Sticta pulmonacea, Peltigera canina, and others,he detected another mode of development of gonidia. All theseLichens are invested either on one or on both surfaces by acortical layer of pseudo-parenchyma. A gradual transition canbe made out between the colourless cells of this tissue andothers, lying internally, with completely green cell-contents(gonidia).

In Pannaria triptophylla the author also detected some in-structive peculiarities. He found that the tubercles on thesurface of the thallus at an early stage contained only one goni-dium, or at most a very few, and in this condition they resembleNostoc-cells or filaments. When these tubercles are maturethey usually are ruptured and through the opening filaments of

152 SYDNEY H. VINES.

gonidia protrude which have a basal heterocyst, and closely re-semble filaments of Eivularia. These observations agree in themain with those of Boruet already mentioned. The authordescribes the development of these tubercles as taking place intwo ways; in the one, they are formed by a coalescence of thehyphse of the thallus to form a group of cells in the manneralready described in speaking of the development of gonidia inCladonia rangiferina, in the other, they are formed from sorediaderived from older tubercles which became invested by hyphse.The mode of origin of the gonidia in the tubercles is similar tothat which takes place in the cortex. From these facts, andfrom the occurrence of numerous gradational forms both as toshape and as to colour, it appears that the gonidia of this Lichenare in reality all of one kind, a conclusion at which Bornet hadalso arrived.

Finally, the author points out the improbability of the viewsheld by van Tieghein and by Weddell as to the existence ofparasitism in Lichens. He considers that the gonidia do notarise from spores which have recently germinated, but from organswhich have a more or less pseudo-parenchymatous structure, aview which finds support in the facts above detailed. He con-cludes that various Protococcacese, Nostocacese, and Rivulariaceseare only certain forms of lichen-gonidia in certain phases oftheir vegetation, and that therefore the gonidia are organs pecu-liar to Lichens.

In the ' Flora' for that year, Winter1 published a paper inwhich he shews that four of the examples adduced by Ko'rber(see ante), in support of his statement that Lichens exisis whichpossess no hyphse, viz., Secologia abstrusa, Sarcogyne privigna,Hymenelia, affinis and Nmtrocymbe faliginea, do, as a matter offact, possess hjphee. In a second publication,8 he exposes theinaccuracy of Korber's statements with regard to Spheeromphaleand its allies, (1) in that hyphae do actually exist in this Lichen,and f 2) in that the spores on germinating do form hyphse and donot, as Korber asserts, give rise directly to gonidia. Theseobservations suffice to answer some of the more important objec-tions—because based apparently upon experimental evidence—brought forward by Korber against Schwendener's theory.

'Nature' for January 27, 1876, contains a commmunicationfrom Lauder Lindsay upon the nature of Lichens. In it hecriticises severely the views of Schwendener and his followers,and repeats his suggestion for the establishment of intermediateand provisional groups of Algo-lichenes and Fungo-lichenes. He

1 ' Zur Anatomie der Kriistenflecliten.'5 ' Ueber die Gattung Sphaeroraphale und Verwandte, Prings, Jahrb. f.

Wiss. Bot.,' Bd. x.

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 1 5 3

points out that there are several difficulties in the natural historyof Lichens with which the Schwendenerians have to deal, as, forinstance, the case of Athalline Lichens that have neither hyphsenor gonidia, that are represented, in fact, only by apothecia—and for examples he refers to Archer's paper which has been con-sidered above. It must be remarked that the author appearsto have overlooked the conclusions at which Archer arrived.He finishes his letter by comparing Schwendener with Bayrhoffer!

An interesting paper was contributed later on in the year byT r̂ank.1 As the result of his observations on the developmentof the gonidia he states that there two ways in which they areformed in the lichen-thallus ; (1) usually they are derived fromthose already existing in the thallus; (£) they make their wayinto the growing thallus from without, and then multiply.Another mode of origin of gonidia was described about the sametime by Minks.2 According to his observations the germinatingspore gives rise to a mass of hyaline hyphse from which, togetherwith the coloured secondary hypha (which is probably connectedwith the development of the apothecia) certain organs are formed,—termed by him Gonangia and Gonocystia—within whichgonidia are formed by free-cell formation.

In passing to the consideration of the papers published in 1877upon this subject it is interesting to recall a sentence whichoccurs in Lauder Lindsay's letter, already quoted. He says : " If,by artificial cultivation, such a union {i.e., of Fungus and Alga)could be made to produce a Lichen, the theory might he held asproven." Such evidence is afforded by Stahl's3 paper on thenature of hymenial gonidia, as the following account willshow.

The experiments which had previously been made in this direc-tion by Reess, Bornet and Treub, had met with only partialsuccess. In all cases the lichen-spores after being sown uponvarious Algae germinated, and their hyphse formed with the Algae,a structure resembling in some degree the thallus of a Lichen,but in no case was any fructification ever developed. Stahl'sresearches upon the hymenial gonidia enabled him to overcomethe difficulties which had marred the success of the experiments ,of his predecessors, and enabled him to trace the whole course^

1 ' Ueb. d. biolog. Verhaltnisse des Thallus einiger Kriistenflechten,Cohn's Beitrage,' Bd. ii.2 'Beit. z. Kennt. des Baues und Lebens der Flechten, ], Gonangiumund Gonocystium,' Wien, 1876.

» ' Beitrage zurEntwickelungs-geschichte der Flechten, 1877.' 1. "Ueberdie geschlechtliclie Fortpflanzung der Collemaceen." 2. "Ueberdie Bcdeu-tung der Hymenial-gonidicn." The first of these papers will be dis-cussed at another time.

154 SYDNEY H. VINES.

of the development of the lichen-thallus from the germinationof the spore to the formation of apothecia.

These hymenial gonidia are, as their name denotes, gonidiawhich occur in the hymenial layer of the apothecium in certainLichens. Nylander seems to have been the first to observe them,and the subsequent investigations of Fuisting and of Winter,have shewn that they originate from the ordinary gonidia of thethallus. They differ from the gonidia of the thallus in that theyare smaller and are of a less vivid colour. The primary objectof Stahl's researches was to account for this difference in appear-between these two kinds of gonidia, and to discover the realsignificance of the presence of gonidia in the hymenium.

The Lichen which he more especially studied was Endocarponpusillum (Hedwig). In its thallus the gonidia, which are of auniform green colour, form a layer lying between the medullaryand cortical parts and extending here and there for a greater orless distance into the cortex. By their mode of division theyindicate their connection with the algal genus Pleurococcus. Theperithecia present the structure which is usually found in pyreno-carpous Lichens. In the spaces between the asci (Fig. 1), and moreor less filling up its whole cavity, is a gelatinous substance which isproduced by the swelling up of the membranes of emptied asci,in which lie the numerous pale-green hymenial gonidia. Theydiffer remarkably in size from the gonidia of the thallus, havinga diameter of only O'OOii—0"004 m.tn., whereas the diameter ofthe latter is from 0'008—O'OISJ m.m. Each ascus usually con-tains two spores of unequal size, the upper one being ratherlarger than the lower. When ripe, they are brown, multicellular,pseudo-parenchymatous structures of considerable size. Whenmoistened, the asci and the gelatinous substance surroundingthem absorb a quantity of water and swell-up. In consequenceof the tension thus produced within the perithecium, the ripeasci burst and expel their spores with such force that they areprojected to a distance of several centimeters.

An examination of the spores which have been thus extrudedshews that they are surrounded by a number of the pale-greenhymenial gonidia. (Fig. 2). If a spore be kept moist, it germi-nates at once after its extrusion, and if it be placed upon a glassslide the whole process can be easily observed. A certain numberof the hyphse which spring from the segments of the sporeinvest the hymenial gonidia by which the spores is surrounded(Fig. 3), and in a few days the invested gonidia shew that theyhave undergone considerable change. The previously scantychlorophyll which gave them a pale-green colour has increased inquantity, so that the enlarged gonidia are uniformly dark-green.A comparison of the free and of the enclosed gonidia shewn in

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 155

fig. 3, cannot fail to suggest that the increase in size exhibited bythe latter must be attributed to the influence of the Fungus.They have ceased to undergo division, whereas the free gonidiahave given rise to numerous individuals. Other hyphse grow andramify, and although they come here and there into contact withgonidia, they do not grow round them, but continue to grow ina straight line along the surface of the slide. These hyphse cor-respond to those which, on a normal substratum (rhizines) pene-trate into it and act as absorbing organs.

The cultures of Endocarpon made in this way, although theplants continued to live for as long as six months, were never sosuccessful as to produce a thallus distinctly differentiated intocortical and medullary portions; apparently the conditions werealtogether too abnormal. An endeavour was made to make theconditions more favourable by substituting for the glass-slide, asa substratum, a piece of porous earthenware, the cavities of whichhad been filled up with soil deposited from suspension in water.Under these circumstance the young thallus presents at an earlystage a differentiation into an upper portion which contains thegonidia, and a lower which is subterranean. (Figs. 4 and 5).The structure of the upper portion is at first very simple, consist-ing of a mass of closely-packed gonidia and hyphse invested bya layer of pseudo-parenchyma, but gradually a differentiationinto a cortical and a medullary part, with an intervening gonidiallayer, becomes apparent. The lower, subterranean portion(hypothallus) consists of colourless, septate, branched and anas-tomosing hyphse, some of which are isolated and others areaggregated in bundles.

Soon after this stage of development has been attained thefirst Spermogonia make their appearance. They are ovoid in formand are completely sunk in the thallus; they contain no gonidia.The first appeared within six weeks after the sowing of the spores,and very shortly afterwards the first formation of perithecia be-came evident. The first spores came to maturity within four orfive months.

The history of the hymenial gonidia which did not becomeinvested by hyphse affords some interesting facts. It has alreadybeen mentioned that they divide, and that the products of theirdivision do not exceed in size the mother-cells from which they arederived. The divisions take place in one direction only, namely,at right angles to the longer axis of the cells, so that the Algaought to be considered in this condition to belong to Naegeh'sgenus Stichococcus, were it not that further observations shew•that these two genera must be united.

Prank has suggested that possibly the gonidia, in consequenceof having been for many generations so intimately associated with

156 SYDNEY H. VINES.

hyphse, have become incapable of active independent vegetation—Stahl does not consider that the facts justify such a view. It istrue that the size of the algal cells which are left to vegetatefreely is, on an average, much smaller than that of the cellswhich are acting as gonidia; but the rapid reproduction of thefreely vegetating Alga cannot co-exist with imperfect nutrition.The differences in size and appearance must probably be attri-buted solely to the various mechanical or physical conditions towhich the Alg8e are respectively exposed.

Observations of a similar nature were made on Thelidiumminululum (Korber). This Lichen made its appearance regu-larly in the cultures of Endocarpon. It could not have made itsway thither by means of soredia, and the only means of account-ing for its appearance is the assumption that it was producedfrom spores which, on germinating, availed themselves of someof the extruded hymenial gonidia of Endocarpon to form athallus. This assumption was proved true by direct experiment.The spores of Thelidium sown in the absence of gonidia gaverise to a mycelium which, so soon as the store of nutriment con-tained in the spore was exhausted, withered away ; but if sownwith gonidia of Endocarpon a fructifying thallus was graduallyformed. In this case also the influence of the Fungus upon theAlga was made apparent by the increased size of the latter, andin the larger amount of chlorophyll contained within it.

Further interesting facts were obtained by the investigation ofPolyblastia rugulosa (Massal.). The spaces between the asci ofthis Lichen (each of which contains usually eight spores) are occu-pied by hymenial gonidia arranged in rows, derived originally fromthe gonidia of the thallus—from which they differ in a verymarked manner, the former being rod-like, the latter more or lessrounded and dividing like the pleurococcoid gonidia of Endo-carpon. If some of the thallus gonidia be cultivated on a slidethey will be seen to divide in successive planes in the threedimensions of space. The products of this division are not,however, rounded cells like those from which they are formed,but are cylindrical and divide only in a plane at right angles totheir length, the segments separating the one from the other.Thus it is possible to obtain from gonidia dividing like PJeuro-coccus the algal form known as Stichococcus. This Stichococcusis identical in form, in size, and in the mode of its division withthe rod-shaped gonidia occurring in the hyinenium.

As in Endocarpon so in Polyblastia, a certain number ofhymenial gonidia are extruded from the peritheciura together withthe spore, which became invested by hyphse when the spore ger-minates. The rod-shaped hymenial gonidia then gradually losetheir cylindrical form, increase in size and assume the rounded

RECENT RESEARCHES INTO THE NATURE OF LICHENS. 157

contour which characterises the gonidia of the thallus of theLichen in question.

The conclusions arrived at as the result of the foregoing inves-tigations are as follows :—(1) in those Lichens which possesshymenial gonidia the thallus is regularly produced by the comingtogether of the spore of the ascomycetous Fungus and the Alga;(2) the hymenial gonidia when actively dividing derive theirnutriment from the constituents of the structure in which theyare enclosed : in view of the small quantity of chlorophyllwhich they contain, it does not seem probable that they give upto the Ascomycete any of the products of their assimilation;(3) if it be suggested that the hymenial gonidia appear to resem-ble the entophytic algal colonies found in Anthoceros, Azolla,Gunnera and others, it must be remembered that they are ofextreme physiological importance in the economy of the Lichenin that they afford to the germinating spores material for theformation of a new thallus.

With this account of Stahl's observations this resume" of thelichen-gonidia discussion must for the present close. It is quiteevident that the theory of the structure of Lichens which wassuggested originally by De Bary and first tested experimentallyby Schwendener is gradually becoming established upon a surefoundation of accurate observations. It will be noticed that theobjections brought against it are, on the whole, more of a theo-retical than of a practical nature. The theoretical objectionsmay be regarded as silenced by the researches above alluded toof Winter, Prank and Stahl, and if further experimental evidencebe required it is to be found in Stahl's paper on the sexual repro-duction of the Collemacese, which will be discussed hereafter.The practical objections are mainly the observations of Arcangeliand of Minks, which seem to shew that gonidia may be deve-loped from hyphse. It must be remarked that although theseobservations tend to prove the same fact, yet they differ widely,and therefore cannot be regarded as being confirmatory the oneof the other. It remains to be seen whether or not other ob-servers will in the future be successful in repeating these observa-tions, and if they will endorse the interpretations which have beenput upon them.

VOL. XVin.—-NEW SER.