321 ALTERNATION OF GENERATIONS IN THE THALLOPHYTES. ' 



do not remaiii in organic connexion ; consequently, it is impossible 

 to regard the "fruits" of Tlialloi3hytes as representing an entire 

 generation. In illustration of this he points out that the 

 zygospores of the Miccorhti are not fructifications comparable to 

 the sjDorogonium of a Moss, but that they are, like those of the 

 Conjf(t/ata', the initial cells of a new generation, and he regards the 

 rudimentary mycelium developed from the zygospore as the 

 "first neutral generation," which differs from the succeeding 

 neutral generations in the very slight development of its vegetative 

 organs. He does not mean to imply that no alternation of 

 generations occurs in the life-history of the Mucorini; on the 

 contrary, he endeavours to show that there is an alternation, not 

 indeed between the zygospore with its rudimentary mycelium and 

 the sexual m3^celium, but between dimorphic sexual and asexual 

 mycelia. He deduces an argument against the current views from 

 Brefeld's observations upon Mucor dicJiotom.ua/'' Brefeld has found 

 that the zygospore of the Mucorini does not give rise in all 

 cases to a simple asexual mycelium as in Mucor Mucedo : in 

 Mucor dichotoinus, when the zygospores germinate under appro- 

 priate culture, they produce well-developed mycelia which bear a 

 number of zygospores. Here then is a case in which the sexually- 

 produced reproductive cell of an oophore gives rise at once to a 

 new oophore, a fact which is obviously irreconcilable with the 

 Moss-type of alternation of generations. Although this fact affords 

 some support to Pringheim's objections to the current views, it is 

 of no positive value as evidence in favour of his own views of the 

 alternation of generations, as will be shown hereafter. In the 

 other grouj) of the Zygosporecv, the Pandorinea, the alternation, 

 according to Pringsheim, is not of a motile sexual coenobium and 

 a resting zygospore, but of sexual and asexual coenobia. 



In applying his views to the OosporecB, he rejects the suggestion 

 of Braun f that the oospore is a rudimentary one- or many-spored 

 fruit, and he regards it as the initial cell of the new^ generation, so 

 that in this Class, as in the i)receding, the alternation is that of 

 dimorphic, independent, sexual and asexual plants. 



Passing on to the Carposporem, we find that in the case of 

 Coleochate, Pringsheim considers the mass of cells formed within 

 the cystocarp to be the "first neutral generation" of the plant, 

 which produces a second neutral generation by means of swarm- 

 spores. "With regard to the other sexual Carjiosporecc, the Ascomy- 

 cetes and the Floridete, he considers that the " fruits " are not to be 

 regarded, any more than those of Colcoclurte, as the direct products 

 of fertilisation, but simply as the female reproductive organs wdiicli 

 have been indirectly affected by it, and which resemble, in this 

 particular, the calyptra of Mosses and the cushion on the prothallia 

 of Ferns. The trichophore and the ascogonium, he urges, are to 

 be regarded as an archegonium which undergoes direct fertilisation, 

 the fertilising influence being conveyed from cell to cell of the 

 organ until it reaches the ascospores. If this view be correct, 



+ ' ]}ot. Zritg.,' JH75, p. SIH. ^. Loc. cit., p. 372. 



