igoS] YAMANOUCHI—APOCAMV IN NEPHRODIVM 309 



phyte number, presented many irregularities in the segmentation 

 divisions and most of the young embryos died after four divisions. 

 Dictyota, then, cannot be regarded as furnishing an instance similar 

 to Nephrodium, since the apogamous developments are abortive and 

 it was not determined whether the structures were sporophytic or 



gametophytic in nature. 



As regards the appUcation of the terms apogamy and parthenogen- 

 esis in the various cases observed, Strasburger's principle (66) is 

 based upon the number of chromosomes contained in the embryo 

 asexually produced; that is, the asexual development of an embr}0 

 from the gametophyte with the diploid number of chromosomes, no 

 matter whether it originates from an egg or a vegetative cell, he calls 

 apogamy; and he regards an unfertilized egg with the diploid number 

 as a vegetative cell. He would restrict the term parthenogenesis to 

 the asexual development of an egg, with the haploid number of chro- 

 mosomes, and with the capabiUty of being fertihzed. Winkler's (76) 

 view is different. He applies the term parthenogenesis to the case of 

 an asexual development of an egg cell, no matter whether it be haploid 

 or diploid, and he proposes to restrict the use of the term apogamy 

 to cases in which the sporophyte is formed as a vegetative outgrowth 

 from the gametophyte. Farmer and Digby's (24) terminology, 

 though not similar, resembles Winkler's. The 

 and parthenogenesis are applied respectively to 

 development of the sporophyte from vegetative cells and from an egg 

 cell of a prothallium produced aposporously ; and to the case where 

 a sporophytic outgrowth is preceded by the fusion of two vegetatiy- 

 -nuclei they apply the term pseudo-apogamy. The apogamy 

 Nephrodium, therefore, would be caUed apogamy by A\ inkler, 

 €uapogamy by Farmer and Digby, and represents no category given 

 by Strasburger. 



ALTERNATION OF GENERATIONS 



Since HoFMEiSTER's investigations we have known that the Ufe- 

 llisto^^' of most plants involves a regular alternation of sexual and 

 asexu'al generations. The subject has been discussed by «iany 

 authors, such as Celakowsky (13, i4, ^S), Sachs (60), Brain 

 <io), Pringsheim (55, 56), Vines (72), De Bary (2), Bo^.ER 



terms 



asex 



e 



