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The genus Pleurotus as an aid for understanding the concept of species in Basidio-mycetes (A. Bresinsky; Regensburg)

Gene for gene speciation, oidia and lethal reactions in Basidiomycete taxonomy(R.F.O. Kemp; Edinburgh)

Interet des cultures dans la delimitation des especes chez les Aphyllophorales etles Auriculariales (J. Biodin; Lyon)

Species and generic-concepts in the Corticiaceae (F. Oberwinkler; Tiibinger)Incidence des caracteres non morphologiques sur la notion d'espece et aut res

taxa chez les macromycetes (H. Romagnesi; Paris)Species concept in Higher Basidiomycetes taxonomy, biology and nomenclature

(R.H. Petersen; Knoxville)Species concept in Agaricales and its adaptation to taxonomy (R. Singer; Chicago)

The formal lectures and the discussions which followed will be published byJ. Cramer and it is hoped will appear in 1977. Prof. R. Kuhner on the Tuesdayevening delivered a public address entitled 'La notion d'espece chez leschampignons superieurs'. This has already appeared separately as a Supplementto Bull. Soc. Linn. Lyon 45 (10) December 1976. Dr. Egon Horak, Zurich was aparticipant but did not deliver a formal paper.

PARALLEL EVOLUTION IN INSECT-DISPERSED FUNGIAND INSECTIVOROUS PLANTS?

Hugo Fletcher

Dr. Yolande Heslop-Harrison (1975) stated that in the five families ofinsectivorous plants: 'constellations of characters have been brought together inthe course of evolution... for successful carnivory'. She also pointed out: 'thateach adaptation for capturing and digesting the prey has its analogue in non-carnivorous plants'.

Having seen Dr. Heslop-Harrison's remarkable scanning electron micro-graphs (1975, 1976) of the glandular hairs of carnivorous plants, I would like tosuggest that there are also fungal analogues of these structures and whereas thenon-carnivorous analogues amongst the Angiosperms may have no connectionwith insects, a number of the fungal analogues appear to be particularly adaptedto dispersal by insects (Fletcher, 1976).

Ingold (1961) discussed various examples of homoplasty in fungi, withparticular reference to seven different 'stalked spore-drops'. Some of these arethought to be adapted by dispersal by insects. Two of Ingold's examples are ofparticular interest: the synnema of Graphlum cuneiforme (= putredinis) and theperithecium of Ceratocystis adiposa. In C. ulmi, the actual organism of the elmdisease, the perithecia appear to be less important in the dispersal of the fungusby the insects, than the Graphium stage, as the synnemata of the latter are pro-duced for most of the year (Pearce, 1962) in the 'galleries' made by the larvae ofthe bark-beetle Scolytus. The synnema of G.ulmi is surmounted by a mucusload containing many conidia. The larvae rub against the mucus heads and carryaway the conidia. The gleaming mucus head of G. putredinis is similar andmoreover bears a striking resemblance to a glandular hair of Drosera, butG. pu tredinis , unlike G. ulmi, is a saprophyte associated with decomposingBrassica and I have not found any reference to its dispersal by insects. I gatheredmy isolate from horse dung (Fletcher, 1975). I regard it to be significant thatthe insectivorous glandular hairs and insect-dispersed fungal structures fall within

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a similar size range (TABLE 1). This could be correlated with the dimensionsof the bodies of insects. In some carnivorous plants the function of the mucuswould appear to be solely a medium in which the spores are more readilydispersed?

TABLE 1. A COMPARISON OF THE HEIGHT OF GLANDULAR HAIRS OF

CARNIVOROUS PLANTS AND REPRODUCTIVE STRUCTURES

IN FUNGI.

ORGANISM STRUCTURES HEIGHT (mm)

I. Drosera capensis Marginal hair on leaf 0.63 to 1.75·"" Central " .... 0 .25 to 0.40

2. Pinguicula grandiflora Stalked gland on leaf 0.18 to 0.323. Ceratocystis ulmi Perithecium 0.5

".. Synnerna (Graphium stage) . 1.04 . Graphium putredinis" O~75 to 1.0

(. in Drosera, some marginal hairs are up to 10.0 mm long)

Speculating on the evolution of these structures: it is thought that the'advanced' insects e.g. Coleoptera (beetles) and Diptera (true flies) first appearedsome 60 million years ago in the Tertiary Period. Two Orders of Angiospermscontaining carnivorous plants: the Sarraceniales and the Tubiflorae may alsohave arisen about this time. The types from which the insect-dispersed fungihave evolved were probably in existence long before the Angiosperms. In thecase of the elm disease, it is possible that the association of the bark beetle withthe fungus is of quite 'recent' origin and that the fungus could have remained aharmless saprophyte without the aid of the beetle. Pathogenic fungi are certainlycapable of 'evolving' very rapidly as seen in the occurrence of the virulent strain'reimported' from the USA, that is the source of the current epidemic (Brasier& Gibbs , 1973).

I am suggesting therefore, that mucus-bearing heads on stalks of whateverorigin and function , are a characteristic feature of adaptation to insects and thatthese structures have arisen many times in the course of evolution.

ReferencesBrasier, C.M. and Gibbs, J .N. (1973) Origin of the Dutch Elm Disease Epidemic

in Britain. Nature. 242,607-609.Fletcher, H.J. (1975) Conidiophore Morphology in Graphium putredinis. Trans.

s-. mycol. Soc. 64,67-71.Fletcher, H.J. (1976) Parallel evolution in plants. B.S.E. News. No.20, 4.Heslop-Harrison, Y. (1975) Enzyme release in carnivorous plants. In Lysosomes

in Biology and Pathology , ed. Dingle, J.T. and Dean, R. 4, A.S.P. Bio-logical and Medical Press, B.V.

Heslop-Harrison, Y. (1976) Enzyme secretion and digest uptake in carnivorousplants. In Perspectives in Experimental Biology. 2. ed. Sunderland, N.,Pergamon.

Ingold, C.T. (1961) The stalked spore-drop. NewPhytologist 60, 181-183.Pearce, T.R. (1962) Pathology of Trees and Shrubs. Oxford.