February 21, 



'«95j 



NA TURE 



401 



of clear protoplasm. He compared this part of the conjugating 

 cell to the "receptive spot " of ihe ovum in the higher Alga:, 

 to the canal-cells of archegoniate plants, and to the synergida; of 

 Angiosperms. 



The conjugation of motile cells has since been observed in 

 many other families of Alga?, of llie most diverse affinities, and 

 in several of these families we can now trace the advance from 

 this primitive fusion of like cell?, to the union of a differentiated 

 ovum and spermalozoid. Pringsheim's discovery has thus proved 

 to have all the far-reaching significance which his scientific 

 insight attributed to it, from the first. It has now become 

 customary to speak of active conjugating cells as "planogamet.v," 

 a word which is useful, as indicating their sexual function, but 

 which must not be allowed to disguise their complete homology 

 with the asexual zoospores. 



In 1S71, he discovered the male plants, and the pre- 

 sumable se.vual cells of Bryofsis, a marine Alga, allied to 

 Vaiicheria : the process of fertilisation however, has not yet 

 been observed. 



Pringsheim's latest contribution to Aigology was his interest- 

 ing work on the course of morphological differentiation in the 

 Sphacelariaceoe, a group ol lirown .*Mga;, in which the progress 

 from filamentous to cormophytic structure can be traced 

 through a very complete series. His views on evolution were 

 akin to those of Nageli {cf. Nature, vol. xliv. p. 5S2). 

 He saw clearly the evidence of descent, but could not admit 

 that natural selection is a sufficient explanation. It seemed to 

 him that the highly differentiated Sphacelaria has nc advantages, 

 in the struggle lor existence, over the simple Ectccaypiis. He 

 held that the first deviations from primitive simplicity of 

 structure, are of a " purely morphological nature," and have no 

 demonstrable relations to any physiological functions. 



Views of this kind are widely spread among German 

 naturalists. The greater, however, our knowledge of the 

 conditions of life in plants becomes, the less room is left for 

 these supposed "morphological characters," which are 

 probably, at most, nothing more than adaptive characters 

 which became fixed a long time ago. 



We have endeavoured to give a connected account of 

 Pringsheim's Algological work. During the same period, 

 however, he had also made important contributions to science, 

 in other directions ; one or two of these must now be noticed. 



A work bearing the date 1S54, on the structure and formation 

 of the vegetable cell, belongs to the period when the doctrine 

 of the multiplication of cells by division had just gained the 

 victory over the erroneous theory of free-cell-formation, so 

 pertinaciously defended by Schleiden. Pringsheim's researches 

 afforded valuable support to the new views. He observed cell- 

 division in both vegetative and reproductive cells of many .-Mga?, 

 as well as in the pollen- mother-cells ol Phanerogams. His 

 view of the formation of the cell-wall comes wonderfully 

 near to the conception of this process, which we have attained 

 at the present day. 



Pringsheim's work on the morphology and development of 

 Salviitia \.i^6'i) is his most important contribution to ourknow- 

 ledge of the higher Cryptogams. He completely worked out 

 the entire life-history of this interesting plant, and a more 

 perfect monograph has never appeared. His observations 

 will always form the basis of our knowledge of Salz'ittia, which 

 is one of the most highly modified forms of Pteridophyta ; they 

 also throw great light on the embryology and development of 

 the class as a whole. 



Pringsheim, in 1876, crowned his long series of morphological 

 investigations by a remarkable essay on the alternation of 

 generations in the Thallophytes, and its relation to that in the 

 Mosses. In the 0|)inion of the writer of this article, this is, 

 from a theoretical point of view, his most important work. 



The essay was suggested by the experiments of its author on 

 the sprouting of Moss-fruits. These experiments were under- 

 taken by Piingsheim with the express object of determining 

 whether the Moss-seta could be induced to subserve vegetative 

 propagation in the same way as the Moss-stem, which it so 

 closely resembles anatomically. He found that the seta of 

 Bryiim and Hypiium, when divided, and kept in moist air, 

 developed a normal ]irotonema, from which true Moss-plants 

 arose. In other words, he succeeded in producing the sexual 

 from the asexual generation, without the intervention of spores, 

 thus establishing the first case of apos/toiy, our knowledge of 

 which has since been so much extended. In the meantime the 

 converse phenomenon of apogaiiiy had been demonstrated by 



NC. I321, VOL. 51] 



De Bary and Farlow, who showed that the asexual generation, 

 in certain Ferns, may arise from the sexual prothallus, without 

 the intervention of the sexual organs. These facts really 

 formed the groundwork of Pringsheim's theory of alternation. 



His leading idea is that the successive generations among the 

 Thallophytes are to be sought in the free sexual and asexual 

 forms of the plant, and not in the plant itself on the one hand, 

 and its fruit on the other. To take only one example ; in the 

 case of the Floride.ie, Pringsheim regarded the tetrasporic and 

 the sexual individuals as constituting the alternate generations ; 

 the sexually produced crystocarp he interpreted, not as a dis- 

 tinct generation, but as a case of polyembryony. Having 

 expanded this view, he proceeds to face the difficulty, how it 

 is to be reconciled with the life-history of the Mosses (in the 

 widest sense), in which the alternation is between vegetative 

 plant and fruit. 



His reply is very ingenious: in the germination of thesexually 

 produced spore of many Thallophytes the young plant sup- 

 presses more or less completely its vegetative stage, and pro- 

 ceeds at once to Ihe formation of asexual spores; this is the 

 case, for example, in CEdi^^oniityn^ SpfucropUa^ HydrodictyoUt 

 and more especially in the Phycomycetous Fungi, in which every 

 transition can be traced between " sporangial " and "mycelial 

 germination of the sexually produced spore. Pringsheim goes 

 on to say : " It may therefore hold good, as a general experience 

 among Thallophytes, that the firit neutral generation hurries 

 by a short road to spore-formanon. suppressing more or less 

 the vegetative part of the plant. ' This change is most marked 

 where germination takes place within the oogonium, as in 

 ColiocJurte. " .\lternation of generations in the Mosses thus 

 appears as a contracted form of that in Thallophytes ; in the 

 former the neutral generations are reduced to a single one, which 

 remains in unbroken connection with the sexual plant. There 

 is therefore no reason for comparing the sporogonium of a Moss 

 wiih the fruits of the Thallophytes," and so on. 



On this view it follows that all alternation of generations 

 must be regarrled as " homologous. " Sporophyte and oophyte, 

 however differently modified, are homologous one with another, 

 both having been derived from sexual and asexual individuals, 

 which at one time presumably differed as little from each other 

 as do the cystocarpic and tetrasporic plants in Red Seaweeds. 

 It is therefore not surprising that in cases of apogamy and 

 apospory, the one generation may still pass over directly into 

 the other. 



These views have been much criticised, and the case is still 

 sill' Jiidice. In England the opposite theory — that the alterna- 

 tion in the higher Cryptogams is " antithetic," the sporophyte 

 being an intercalated generation, not homologous with the 

 ocrphyte, is predominant, and appears to receive some support 

 from certain minute histological differences between the two 

 generations. Pringsheim's interpretation of the facts has, how- 

 ever, some advantages, perhaps the most conspicuous among 

 which is that it would enable us to understand the existence of 

 the immense and unbridged gulf which separates the sporophyte 

 of the Muscineae from that ol the Vascular Cryptogams. "The 

 latter might well have been derived from ancestors, in which 

 the " first neutral generation " had never suffered the extreme 

 reduction which characterise it in the Moss series, but h.id 

 always retained its vegetative organs. It would then no longer be 

 necessary to endeavour to force the plant of a Fern or a Horsetail 

 to fit into the Procrustean limits of a Moss-sporogonium. 



We have endeavoured to give some idea of Pringsheim's 

 varied activity in the field of morphology, which he cultivated 

 with unsurpassed success. It remains to say a few words 

 regarding his physiological investigations, though these are far 

 from possessing the same importance. 



So far as we have been able to find, Pringsheim's first entry 

 upon the physiological domain dates from the year 1S75, when 

 he published papers on the spectrum of chlorophyll, and on 

 the modifications of th.it pigment. His dclnif as a physiologist thus 

 almost exactly coincides with the climax of his brilliant career as 

 a morphologist. It was not till 1S79, however, that he became 

 prominent in physiological questions. In that year he produced 

 his first paper on the action of light and the function of 

 chlorophyll. He investigated the action of light of great in- 

 tensity on vegetable tissues, and observed the consequent de- 

 struction of the chloroph)ll, in green tissues, and the disorgan- 

 isation of the protoplasmic structures, both of which he attri- 

 buted to excessive oxidation.- The great conclusion at which 

 he arrived, is that " the function of chlorophyll, by means of 



