No. 503] XOTES AND LITERATURE 



747 



where gametophytes have the sporopbytic number of chromo- 



A third paper which should be mentioned in connection with 

 these two on types of honiosporous ferns is Strasburger's 3 study 

 of apospory in heterosporons Marsilia. Parthenogenesis had 

 been reported by Shaw as occurring in of) per cent, of the female 

 gametophytes of Marsilia Drummondii. Xathansohn had in- 

 duced parthenogenesis in Marsilia vestita and .]/. macro, by keep- 

 ing germinating megaspores at a temperature of 35° C. for 24 

 hours and then" allowing them to continue their development 

 at a temperature of 27° C. Under this treatment the eggs of 

 7-12 per cent, of the spores gave rise to embryos parthenogenet- 

 ically while at lower temperatures embryos were only developed 

 after fertilization. 



Strasburger found that in Marsilia Drum mondii the nuclei 

 of the female gametophyte contain 32 chromosomes which is the 

 sporopbytic or diploid number present in various vegetative 

 regions of the sporophyte. The process of sporogenesis pre- 

 sents various irregularities: the number of niegaspore mother- 

 cells is less than 16 and at times only 4: sometimes the mitoses 

 within these cells are reduction divisions of the usual type 

 (heterotypic), but in other cases spores are formed only through 

 vegetative mitoses in which the sporophyt ie or diploid number 

 of chromosomes (32) is retained. Such spores give rise to 

 female prothallia with eggs having the sporopbytic number of 

 chromosomes and a parthenogenetic development of the latter 

 follows. These conditions differ from those of apospory in the 

 fact that spores are developed, but agree in the final result that 

 the process of chromosome reduction is suppressed in the life 

 history. The microspores showed irregularities in their develop- 

 ment and on germination did not produce mature sperms. Two 



other species in the genus. MarsUlia macro and M. Xardu, pre- 



Perhaps the most important feature of this cytological re- 

 search on apogamy is its bearing on current theories of the 

 nature and basis of alternation of generations in plants. It 

 is perhaps rather generally held by those who accept the anti- 

 thetic theory that the differences between sporophyte and game- 



