The REPRODUCTION of LICHENS and the SEXUALITY of the ASCOMYCETES. By SYDNEY H. VINES. M.A., Christ's

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1 438 SYDNEY H. VINES. in which they lie. This point is called attention to in my ' Monograph on Elasmobranch Fishes/ page 39, where it is stated that " the network in favorable cases may be observed to be in connection with the nuclei just described. Its meshes are liner in the vicinity of the nuclei, and the fibres in some cases appear almost to start from them." The nuclei in the yolk are knobbed bodies divided by a sponge work of septa into a number of areas each with a nucleolar body. The REPRODUCTION of LICHENS and the SEXUALITY of the ASCOMYCETES. By SYDNEY H. VINES. M.A., Christ's College, Cambridge. With Plate XX. IN a previous number of this Journal 1 an account was given of the present state of the " lichen-gonidia question." in which especial reference was made to the researches of Stahl into the significance of the gonidia occurring in the hymenium of various lichens. Those researches, it was pointed out, afforded stroug evidence in favour of Schwendener's theory of the nature of lichens. Stahl's further researches, 2 of which a brief resume will here be given, into the processes of their reproduction, seem to place the soundness of this theory beyond reasonable doubt. No less than four distinct organs have been discovered at various times in the thallus of lichens, all of which have been regarded as being connected with their reproduction, viz. (1) Soredia, (2) Spermogonia, bearing Spermatia, (3) Apothecia, containing asci in which spores are formed, (4) Pycnidia, giving rise to Stylospores. The Soredia were first mentioned by Acharius, 3 their structure was accurately described by Tulasne,* and their development was fully made out by Schwendener. 5 Their significance appears to have been also completely understood by Wallroth and Meyer. A soredium consists of one or more gonidia surrounded by a mass of hyphse, and when it is 1 April, s ' Ueb. die Geschleohtliche Portpflanzung der Collemaoeen,' ' Lichenographia Universah's,' L. K. Ttilasne, ' Mem. sur les Lichens,' 1852, p In Nageli's ' Beitr. zur Wiss. Bot,' Heft, ii, 1860; also, ' JFlora,' 18G3.

2 REPRODUCTION OF THE LICHENS. 439 thrown off from the thallus, it directly grows into a new individual. The other organs are of more complicated structure, and until recently, their significance was by no means fully understood. The Spermogonia were first recognised as being distinct organs by Itzigsohn, 1 who believed them to be antheridia containing motile antherozoids. Tulasne, however, pointed out that the spermatia with which they are filled are not motile, and that the movement observed by Itzigsohn was merely molecular; he considered that they were cornparable to the non-motile antherozoids of the Florideas. More recently Cornu 2 has shown that spermatia may be in duced to germinate when they are placed under favorable conditions, and he is therefore inclined to regard them as conidia developed in special receptacles, which differ from the ordinary conidia in size only. In the introductory paragraphs of his paper Stahl argues in opposition to the views of Cornu that the fact of their having germinated is no absolute proof of the non-sexual nature of the spermatia, and he appeals to the growth of pollen-tubes in solutions of sugar in support of his argument. 3 He also points out that Cornu was unsuccessful in inducing the germination of spermatia derived from lichens. The facts upon which Stahl bases his argument in favour of the sexual nature of the spermatia of lichens will be stated in considering the development of the apothecia. The structure of the Apothecia had been carefully investigated and described by Tulasne in his above-mentioned work. Schwendener* had shown that the hyphae from which the asci were developed were independent of those which bore the paraphyses, and Fuisting 5 had distinguished the former group of hyphse as " ascogenous hyphae," and had shown that the excipulum and the paraphyses were developed from the same kind of hyphal filaments, but no accurate knowledge as to the very earliest stages of. their development had been obtained until the publication of Stahl's researches. Possibly, as he himself points out, the early stages of development 1 'Bot. Zeit.,' Up to this time the Spermogonia had been regarded as distinct genera of Lichens, Pyrenotheca (Fries), Throtnbium (Wallroth), just as the Soredia had been regarded by Acharius as forming the genus Variolaria. 5 Ann. d. Sci. Nat.,' se>. vi, t. iii, See the recent observations of Tomaschek, " Ueb. die Entwick. Her Polletipfliinzelieii des Colcliicum Autumnale." ' Siuber. d. k. Akad. d. Wiss.,' Ixxvi, 1877, Wien. * 'flora,' 'Bot. Zeil.,' 1S68.

3 440 SYDNEY H. VINES. which he describes, had been seen, but had been misinterpreted by Gibelli. 1 In the thallus of Collema microphyllum, Stahl detected certain organs to which he gives the name of Carpogonia. Each carpogonium consists of a hyphal filament deeply placed in the thallus, which is coiled on itself (generally two or three tiroes), and is then continued straight to the free surface of the thallus, above which its terminal cell projects (Fig. 1). To the spirally wound portion he gives the name of Ascogonium, to the straight portion that of Trichogyne. Not unfrequently spennatia could be seen adhering in considerable humber to the projecting (Fig. 2, a) cell of the trichogyne. It will be readily understood that they must h»ve been conveyed there by means of water. In some cases Stahl was able to detect (Fig. %, b) a canal which placed the contents of the spermatium in connection with those of the terminal cell of the trichogyne. The result of this is that the cells of the trichogyne wither and disappear, and that certain processes of growth of the cells of the ascogonium are initiated, which may be briefly described as follows : The cells first of all increase in size, and then they undergo division. As a result of this the spiral arrangement of the cells becomes less and less conspicuous, for the cells gradually separate from one another. Whilst these changes have been taking place in the ascogonium, it has become invested by a dense felt-work of hyphse formed by the active growth of the hyphae of the thallus. From this investing layer hyphse grow inwards between the separating coils of the ascogonium and bear paraphyses, which form the rudimentary hymenium. At the same time outgrowths have been formed from the cells of the ascogonium, which either are asci or grow into hyphal filaments, which bear asci as lateral branches (Pig. 3). The asci, whether derived direitly or indirectly from the cells of the ascogonium, come to lie in the hymenium among the paraphyses. At this period of its development the apotheciutn possesses all the elements which usually enter into its composition. Most externally is a dense layer of interlaced hyphae forming the hypothecium, the inner portion of which consists of a layer of pseudo-parenchymatous tissue, the excipulum proprium, within this is the layer of ascogenous filaments, and most internally lies the hymenium consisting of paraphyses derived more or less directly from the hypothecium and of asci derived more or less directly from tbe ascogonium. In various species of Physma, Mass. (Lempholemma, 1 ' Nuov-giorn. Bot. Ital./ 1870.

4 REPRODUCTION OF THE LICHENS. 441 Korher), the ascogonia are formed in immediate proximity to the spermogonia, hut in other respects they resemble those of Collema, and their subsequent history is the same. It appears from these observations that the development of the apothecia of lichens is the resalt of the fertilisation of carpogonia by means of spermatia. Cottema pulposum affords negative evidence in support of this statement, for in large thalli of this Lichen Stahl was unable to find any spermogonia, and at the same time he failed to detect any indications, of developing apothecia. His investigation of Syneehoblastus conglomeratus, of Leptogium Hildenbrandii and microscopicum, and of such heteromerous Lichens as Parmelia stellaris and pulverulenta completely confirmed the above conclusions. The resemblance existing between the apothecia of lichens and the fructifications of ascomycetous fungi had long been remarked. Now that the development of the apothecia has been completely traced, and their origin from the colourless filaments only of the thallus (except in so far as the gonidia of the thallus give rise to hymenial gonidia) has been placed beyond doubt, there is sufficient evidence to justify a classification which places lichens among the Ascomycetes in the class Carposporeae. Collateral evidence is obtained by a coinparison of the mode of fertilisation of the carpogonia of lichens with that of the Floridea. In both groups the sexual cells are completely differentiated, and in both the male cells are not motile. Stahl very naturally suggests the propriety of calling the male cells of the Floridese not antherozoids, but spermatia. The evident sexuality of the lichens has an important bearing upon the vexed question of the sexuality of the whole group of the Ascomycetes, to which they are now attached. The carpogonium of Ascoboltcs furfur aceus 1, one of the Discotnycetes, resembles in some respects that of Collema, and the resemblance of the ascogonium of Eurotium 3 and of Sordaria 3 to that of Collema is most striking, but the carpogonium of the lichen is peculiar in that it possesses a trichogyne. In the above-mentioned Ascomycetes fertilisation is effected not by spermatia, but by a kind of conjugation of the ascogouium with another filament, the 1 Janczewski, "Morpb. Uaters. ub. Asoobolus furfuraceus." 'Bot. Zeitff.,* De Baiy, 'Eurotium, etc., nebst Bemerkungen uber die Geschlech:sorgane der AsGomyGeteu,' ' Gilkinet, ' Keck Morphol. sur les Pyr6aomyc6tes,' J. Sordari6es, 1874.

5 442 SYDNEY H. VINES. pollinodium ; consequently the formation of a trichogyne is unnecessary. Doubt has, however, been cast upon this interpretation of the coalescence of these two filaments. Van Tieghem l considers that, in Eurotium at any rate, this apparently sexual act is merely an instance of a coalescence of hyphal filaments which is by no means uncommon, and his observations upon Chsetomium lead him to conclude that not only is such a coalescence unnecessary for the formation of a fructification, but that it tends rather to prevent it. Brefeld 2 also pronounces against the sexuality of the Ascomycetes. He found that ascogenous hyphse removed from the developing fructification and cultivated in solutions of salts did not form asci, but simply grew out into ordinary hyphal branches. Stahl, in reply to Brefeld's arguments, points out that the development of the one generation from the other is not necessarily connected with the formation of sexual cells or of spores. In mosses, for instance, Stahl 3 and Pringsheim 4 have shown that the cells of the sporogoniam will, under certain circumstances, grow out into protonemal filaments upon which new moss-plants are developed. Here the transition from the one generation (sporophore) to the other (oophore) is effected independently of the spores. In the ferns it appears, from the researches of Farlow, 5 that the prothallus (oophore) may produce a young fern (sporophore) by simple budding without any formation of archegonia. These facts suffice to overthrow the argument founded by Brefeld upon his observations. The forms of ascomycetous fungi, studied by Van Tieghem and by Brefeld (Peziza, Morchella), apparently do not present that distinct origin from separate groups of hyphse of the paraphyses and of the asci, which is so prominent a feature in the development of the apoihecium of a lichen, and their sexual organs are undeveloped. In the lichens, and some other Ascomycetes, which may be regarded as being the most perfectly developed forms of this group, the evident differentiation accompanying the first formation of the apothecium is accompanied by a well-marked sexuality. 1 ' Sur le dev. du fuit des Cbsetomoum et la pretendue sexualit6 des Ascomycetes,' '' Die Eatwickelunesgeschichte der Basidiomyceten." ' Bot. Zeifc., " Ueb. Protonemabildunar an. dem Sporogonium der Laubmoose." 'Bot. Zeitg., " Ueb. Sprossung der Moosfriichte, &c." ' Jalirb. f. Wiss. Bot.,' See this Journal, vol. xiv, 1874.

6 THE REPRODUCTION OF LICHENS. 443 In a second group, including the Erysipbese, Eurotium, and others, the differentiation of paraphyses and asci is not so evident, and the sexuality is less marked. In a third group, including Morchella, Peziza, and others, this differentiation does not present itself, and the sexuality cannot be detected. A very striking instance "of this has been described by Bauke 1 in Pleospora herbarum, one of the commonest of the Spheeriacese (Pyrenomycetes). The formation of the peritheciurn commences with the enlargement and subsequent division of usually several adjacent cells of a hypha, which may be regarded as a female organ, a carpogonium, but not an ascogonium. In this way a rounded mass of cells is produced, which becomes of a deep brown colour on the exterior. This stage is usually reached in four or five days from the commencement of development, but it is three or four weeks before the formation of the " nucleus," more accurately, of the paraphyses, begins. A number of thin, closely-packed hyphse, grow out from certain of the parenchymatous cells which lie at about the same level near the base of the young perithecium. These hyphse absorb not only the contents of the cells forming its central portion, but their thickened cell-walls as well; they seem to perform the same function as the de icate hyphee, which grow out from the ascogonium of Penicillium. The perithecium may undergo a period of inactivity, but this is by no means necessary, before the asci are formed. They arise as outgrowths from the basal cells of the puraphyses. Preparations which show the development of the young asci very clearly present no appearance which could possibly indicate anything like a sexual process. It appears, therefore, that certain Ascomycetes are distinctly sexual, whereas others are distinctly asexual. The absence of distinct sexual organs may be accounted for either by considering the members of the group in which they do not occur as primitive forms which have not reached a sufficiently high stage of development for such a differentiation, or (and this is, perhaps, the more probable assumption) by regarding them as degraded forms which have lost the sexuality which more primitive forms still retain. It remains to consider briefly the significance of the pycnidia. Their existence in lichens was first discovered by Tulasne 2, and he points out that the presence of them 1 " Zur Entwickelungsgeschichte der A.scomyceten." ' Bot. Zeit.,' 1S77 3 Loc. oit., p. 107.

7 444 SYDNEY H. VINES. affords fresh proof of the close affinity which exists between these plants and the ascomycetous fungi. He had already shown that his predecessors were mistaken in regarding the pycnidia of these fungi as distinct individuals, forming the genera Phoma, Diplodia, Sphseropsis, &c., and had suggested that, since they occur upon the mycelium with the perithecia, they are probably organs of some kind belonging to the fungus. De Bary's researches upon Cicinnobolus 1 threw doubt upon the correctness of Tulasne's suggestion. It seemed to be absolutely certain that Erysiphe and Cicinnobolus belonged to the same mycelium, that they were ire fact, different organs of the same plant; but De Bary proved that this was really a case of parasitism, that the mycelium of Cicinnobolus was parasitic upon that of Erysiphe. Under these circumstances it was still possible to argue that the pycnidia might after all be distinct fungi parasitic upon the mycelium bearing them. An elaborate investigation into the development of the pycnidia has recently been made by Bauke 2 with the most conclusive results. Mycelia formed by the germination of the ascospor.es of Pleospora polytricha, Cucurbitaria elongala, and Leptosphcerid {Pleospora) Doliolum, regularly produced pycnidia, and the connection of the pycnidium with the ascosporewas in each case satisfactorily ascertained. It must, therefore, be concluded tviat the pycnidia do not form a distinct group of fungi, but that they belong to the Ascomycetes. These pycnidia, in the course of their development, presented appearances which recalled the formation of the perithecium of Ascobolus and of other ascomycetous fungi. In Pleospora herbarium the mode of development of the pycnidium, so far as the formation of the stylospeors, is essentially the same as that of the perithecium. These facts suggest, as Bauke 8 points out, that a genetic relatio nship exists between these two forms of fructification, and he goes on to inquire if the pycnidia and the perithecia may not be regarded as alternate generations. According to the views recently propounded by Pringsheim, 4 as to the alternation of generations in Thallophytes, the morphological analogues of the two alternate generations of Cormophytes, are to be found in the independent neutral and sexual indi- 1 De Bary and Woronin, ' Beit. z. Morpbol. uad Physiol. d. Pilze,' iii. Heft, s 'Beitr. z. Kenntniss der Pjcuiden, Nova Acta. d. k. Leop.-Carol Akad.,' Bot. Zeitung,' * ' Jahrb. f. Wiss. Bot.,' d. xi, Heft 1, 1877

8 KEPK0HUCT1ON OF THE LICHENS. 445 viduals of Thallophytes. If this be so, the mycelium and the " fruit" of the Ascomycetes cannot be regarded as the two distinct generations, but the fruit which has been produced sexually belongs to the same generation as the mycelium bearing it, and the second neutral generation begins, instead of ending, with the spore. Pringsheim suggests that the pycnidia represent the neutral generation of the Ascomycetes, and that probably the irregular succession of these two forms indicates an incomplete, as it were, preparatory form of the alternation of generations. These suggestions seem to be supported by Bauke's observations upon Pleospora herbarum, for here perithecia and pycnidia appear to be distinct generations, and their succession is extremely irregular. Bauke explained the similarity in the development of pycnidium and perithecium on the hypothesis that the pycnidium was derived by adaptation from the perithecium at a time when the latter had already attained its present development, and that an alternation of generations became apparent at a later period. Pringsheim prefers to consider that both pycnidium and perithecium in, fact all the sexual and neutral fructifications of Thallophytes, are simply the result of modifications taking place in particular directions of a single primary fructification, the neutral sporangium. EXPLANATION OF PLATE XX. FIG. 1. Section of thallus of Collema Microphyttum. a. The projecting cell of the trichogyne. TIG. 2. a. Spermatia surrounding the terminal cell of the trichogyne. b. Coalescence of a spermatium with the terminal cell of the trichogyne. FIG. 3. Young apotheciam of Collema Microphylluru. a. Excipulum fchallodes. b. Excipulum proprium. c. Hypothecium. The hymenium consists principally of paraphyses, between which young asci are being formed from ascogenous hyphce.