538 



NATURE 



[OCTOIIKR I, 1896 



bearing a sporangium, or may itself turn at once into a 

 sporangium (producing zoospores) without any vegetative 

 development. Here it seems certain that Pringsheim's view is 

 the right one, for all stages in the reduction of the first neutral 

 generation lie before our eyes. Nowhere, either here or among 

 the green .Mg.v, do I see any evidence for the intercalation of a 

 11CW generation or a new form of s]5ore on the germination of 

 the fertilised ovum. 



I'ringsheim extends the same view to the higher plants. The 

 sporogonium of a moss is for him the highly modified first neutral 

 generation, homologous with the vegetative plant, but here 

 specially adapted for spore-formation. I have elsewhere pointed 

 out (Natukk, February 21, 1895) that this view has great 

 advantages, for not only does it harniorise exactly with the 

 actual facts observed in the green Algii; and their allies, but it 

 also helps us to understand the astoundingly different forms 

 which the archegoniate sporophyte may assume. 



It seems to me that Pringsheini was right in regarding the 

 fruit-formation of Floridere as totally different from the sporo- 

 ])hyte-formation of Coleodudc or the Bryophyta. The cystocarp 

 bears none of the marks of a distinct generation, for throughout 

 its whole development it remains in the most complete organic 

 connection with the thallus that bears it. The whole Floridean 

 process, often so complicated, appears to be an arrangement for 

 effecting the fertilisation of many female cells as the result of an 

 oiiginal impregnation by a single sperm-cell. There is here still 

 a great field for future research ; but in the light of our present 

 knowledge there seems to be no real parallelism with the 

 formation of a sporophyte in the higher plants. 



The gap between the Bryophyta and the Alga: remains, 

 unfortunately, a wide and deep one, and it is not probable that 

 any Algce at present known to us lie at all near the line of 

 descent of the higher Cryptogams. Kiaia is often compared 

 with Coleoclucte, but it is by no means evident that Kiccia is a 

 specially primitive form. In Aiil/wceros, which bears some 

 marks of an archaic character, the sporophyte is relatively well 

 developed. To those who do not accept the theory of inter- 

 calation it is not necessary to assume that the most primitive 

 Bryophyta must have the most rudimentary sporophyte. 



Apart from other differences, Bryophyta differ from most 

 green Alga; in the fact that asexual spores are oii/y found in the 

 generation succeeding fertilisation. The spores moreover are 

 themselves quite different from anything in Alga:, and the 

 constancy of their formation in fours among all the higher 

 plants from the liverworts upwards, is a fact which requires 

 explanation. I should like to suggest to some energetic 

 histologist a comparison of the details of spore-formation in the 

 lower liverworts and in the various groups of Algae, especially 

 those of the green series. It is possible that some light might 

 be thus thrown on the origin of tetrad-spore-formation, a subject 

 as to which Prof. Farmer has already gained some very remark- 

 able results. On Pringsheim's view some indications or homo- 

 logy between bryophytic and algal spore-formation might be 

 expected, and anyhow the tetrads require sonic explanation. 



The peculiarities of the sporophyte in the Archegoniata:, as 

 compared with any algal structures, depend, no doubt, on the 

 acquirement of a terrestrial habit, while the oophyte by its mode 

 of fertilisation remains " tied down to a semi-aquatic life." 

 (Bower, "Antithetic Alternation.") Prof. Bower's phrase 

 "amphibious alternation" expresses this view of the case very 

 happily, and indeed his whole account of the rise of the 

 sporophyte is of the highest value, even though we may not 

 accept his assumption as to its origin de novo. 



I attach special weight to Prof. Bower's treatment of this 

 subject, because he has shown how the most important of all 

 morphological phenomena in plants, namely the alternation of 

 generations in Archegoniat;e, may be explained as purely 

 adaptive in origin. All Darwinians owe him a debt of 

 gratitude for this demonstration, which holds good even if we 

 believe the sporophyte to be the modification of a pre-existing 

 body, and not a new formation. 



Al'OSI'ORV AND Al'OGA.MY. 

 We must ren>ember that the theory of homologous alternation 

 has twice received the strongest confirmation of which a 

 scientific hypothesis is susceptible — that of verified prediction. 

 In both cases Pringsheini was the happy prophet. Convinced 

 on structural grounds of the homology of the two generations in 

 mosses, he undertook his experiments on the moss-fruits, in the 

 hope, as he says ("Ges. Abh." II., p. 407), tliat he would 



NO. 1405, VOL. 54] 



.succeed in producing protonema from the subdivided seta of the 

 mosses, and thus prove the OTor/Zjo/iy/cn/ agreement of seta and 

 moss-stem. His experiment, as everybody knows, was com- 

 pletely successful, and resulted in the first observed cases of 

 apospory, i.e. the direct outgrowth of the sexual from the 

 asexual generation. 



Here he furnished his own verification ; in the second case it 

 has come from other hands. In the paper of 1S77. so often referred 

 to, he says (p. 391) : " Here, however \i.f. in the ferns], the act of 

 generation, that is, the formation of sexual organs and the origin 

 of an embryo, is undoubtedly bound up with the existence of 

 the spore, iiiilil those future ferns are found which I indicated as 

 conceivable in my preliminary notice, in w/iiili the prothallus 

 ■will sprout forth directly from the frond.'' 



It isunnecessary.to remind English botanists that Pringsheim's 

 hypothetical aposporous ferns are now perfectly well known in 

 the flesh ; such cases having been first observed by Mr. Druery 

 and then fully investigated by Prof. Bower. 



A very remarkable case of direct origin of the oophyte from 

 the sporophyte has lately been described by Mr. E. J. Lowe, in 

 a variety al Scolopendriuni vul^^are. Here the young fern-plant 

 ]iroduced prothalli bearing archegonia as direct outgrowtlis from 

 its second or third frond. The specimen had a remarkable 

 history, for the young plants were produced from portions of a 

 prothallus which had been kept alive and repeatedly subdivided 

 during a period of no less than eight years. I cannot go into 

 the interesting details here, they will be iniblished elsewhere ; 

 but I wish to call attention to the fact that in this case the pro- 

 duction of the sexual from the asexual generation, occurring so 

 early in life, has no obvious relation to suppressed spore-forma- 

 tion, and so appears to differ essentially from the cases first 

 described, which occurred on mature plants. I believe Mr. 

 Lowe's case is not an altogether isolated one. 



The converse phenomenon — that of apugauiy — or the direct 

 origin of an asexual plant from the prolhalKis without the inter- 

 vention of sexual organs, has now been observed in a consider- 

 able number of ferns, the examples already known belonging to- 

 no less than four distinct families : Polypodi.acea:, Parkeriaces, 

 Osmundacea?. and Hymenophyllacea;. In Trichomanes alatum 

 Prof. Bower found that apospory and apoganiy co-exist in the 

 same plant, the .sporophyte directly giving rise to a prothallus, 

 which again directly grows out into a sporophyte ; the life-cycle 

 is thus completed without the aid either of sjiores or of sexual 

 organ.s. Dr. W. H. Lang, who has recently made many interest- 

 ing observations on apogamy, will, I am glad to say, read a 

 paper on the subject before this .Section, so I need say no more. 

 I must, however, express my own conviction that the facility 

 with which, in ferns, the one generation may pass over into the 

 other by vegetative growth, and that in both directions, is a 

 most significant fact. It shows that there is no such hard and 

 fast distinction between the generations as the antithetic theory 

 would appear to demand, and in my opinion weighs heavily on 

 the side of the homology of sporophyte and oophyte. I cannot 

 but think that the phenomena deserve greater attention from 

 this point of view than they have yet received. 



A mode of growth which affords a perfectly efficient means of 

 abundant propagation cannot, I think, be dismissed as merely 

 teratological. 



Since the foregoing paragraph was first written Dr. Lang has 

 made the remarkable discovery (already communicated to the 

 Royal Society) that in a Lastnca sporangia of normal structure 

 are produced on the prothallus itself, side by side with normal 

 archegonia and antheridia. I cannot forbear mentioning this 

 striking observation, of which we shall hear an account from the 

 discoverer him.self. 



The strongest advocate of the homology of the prothallus 

 with the fern plant could scarcely have ventured to anticipate 

 such a discovery. 



KeLATIOX BETWEIiN MOSSES AMi FeRNS. 

 Goebel said, in 1882: "The gap between the Bryophyta and 

 the Pteridophyta is the deepest known to us in the vegetable 

 kingdom. We must seek the starting-point of the Pteridophyta 

 elsewhere than among the Muscime : among forms which may 

 have been similar to liverworts, but in which the asexual genera- 

 tions entered from the first on a different course of development." 

 (Schenk's " Handbuch der Botanik," vol. ii. i>. 401.) I cannot 

 help feeling that all the work which has been done since goes to 

 confirm this wise conclusion. Attempts have been made in the 

 1 most sportsmanlike m.anner (to adopt a phrase of Prof. Bower's) 



