ii6 Plant Genetics 



a new individual. This behavior of ferns is particularly 

 interesting on account of the chromosome situation 

 involved. Since the gametophyte is an x structure and 

 the sporophyte a 2X structure, when apogamy was first 

 discovered it was taken for granted that in some way 

 nuclear fusion had occurred and the 2X number obtained. 

 More recent work, however, notably that of Yama- 

 NOUCHi (2), showed that the apogamous sporophyte is 

 an X structure, and such a sporophyte produces spores 

 without the reduction division. 



Ferns are also aposporous, which means the formation 

 of gametophytes by vegetative cells of the sporophyte, 

 the gametophyte in such a case being a 2X structure. 

 With the phenomena of apogamy and apospory estab- 

 lished, the question naturally rises as to their bear- 

 ing upon the machinery of Mendelism, involving the 

 reduction division and the segregation of hereditary 

 factors. 



Seed plants, however, are of particular interest, since 

 they have furnished the chief material for work in 

 genetics. Many cases of parthenogenesis and vegetative 

 apogamy in seed plants have come to light. It is an 

 interesting fact that, although these cases are well dis- 

 tributed throughout the groups of seed plants, they seem 

 to be especially numerous among the Compositae. In 

 many cases, therefore, the embryos of seed plants are 

 produced by unfertiUzed eggs or other cells, as in Anten- 

 naria, Hieracium, Taraxacum, Thalictrum, etc. Some 

 of the best known cases were subjected to cytological 

 investigation, and it was found that in most cases the 

 parthenogenetic egg is diploid {2x), thus containing the 

 sporophyte rather than the gametophyte number of 



