No. 464.] STUDIES ON PLANT CELL.— VI/. £;6l 



of chromosome reduction during the formation of the embryo- 

 sac seems to offer an explanation of other examples of apogamy 

 presented by the embryo-sac. Thus apogamous developments 

 of embryos from synergids as in Alchemilla sericata (Murbeck, 

 : 02) or from antipodals as in Allium odorum will not seem 

 strange if reduction processes are suppressed in the production 

 of an embryo-sac and its nuclei retain the sporophyte number of 

 chromosomes. Such nuclei have in them the same potentialities 

 of development as do those of the nucellus whose cells form 

 embryos vegetatively and entirely independent of gametophytic 

 activities in a number of forms {e. g., Funkia, Coelebogyne, 

 Citrus, Opuntia, Alchemilla pastoralis, etc.). This type of 

 apogamy from a gametophyte which retains the sporophyte 

 number of chromosomes may be found to hold a very close 

 relation to apospory for there is the same reduction or omission 

 of the processes of sporogenesis as is found in that phenome- 

 non. However, since we know nothing of the cytological events 

 of apospory it is unwise at present to follow the speculation 

 further. 



The peculiarities of parthenogenesis in the spermatophytes do 

 not seem so remarkable since the discoveries recorded above. It 

 is not strange that an e^gg should form an embryo without fer- 

 tilization when its nucleus contains the sporophyte number of 

 chromosomes. The most remarkable feature in this suppression 

 of reduction phenomena in Antennaria, Thalictrum, and Alche- 

 milla is the possibility of developing an embryo-sac with nuclei 

 in the number and arrangement typical of the female gameto- 

 phyte and yet with the sporophyte count of chromosomes. The 

 embryo-sacs with their contents have clearly the morphology of 

 female gametophytes and must be so considered in spite of the 

 fact that their nuclei contain twice as many chromosomes as 

 usual. It is clear that the potentialities of sporophyte and 

 gametophyte involve other factors besides those of the chromo- 

 some count. This is a very important conclusion because we 

 have been accustomed to lay great weight on the number of 

 chromosomes as the cause of sporophytic and gametophytic 

 developments respectively. We must recognize the presence of 

 other factors determining alternation of generations besides the 

 chromosomes. 



