1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 



347 



might under favorable conditions be the starting point of 



which would be similar to certain mutant 



The 



case of Oenothera gigas (see De Vries, '03, '13) a mutant from 

 Oe. Lamarckiana with double the number of chromosomes is 

 similar. 1 Other tetraploid mutants are known (see Gates, 



the 



the diploid gametophyte and tetraploid sporophyte of 

 es produced experimentally by Marchal ('09, '11) is 



in- 



teresting in this connection. 



Now, the possibility of a similar double fertilization in an as- 

 comycete is not, a priori, excluded. There might be an isolated 



exam 



But the normal expectation is that it would 



afterward a nuclear history in its ontogeny similar to others 



with one nuclear fusion and one reduction from 

 it is not likely that the entire group of sac 

 on such a mutation, followed by a double reduction 

 division and then double fertilization again and s 



Lx. But 

 founded 



eral 



where it has been 



The 



well established that 



o nuclear fusion prior to the ascus, together with 

 uniformity of the ascus nuclear phenomena in the 

 atroverts the idea of anv such origin for the sac 



group, controverts 



fungi. 



All of these facts go to prove that the inclusion and fusion 

 of two nuclei in the young ascus is of a very different and far 

 greater significance than a vegetative one. The process of 

 nuclear fusion in the ascus does not comprise in itself the 

 entire series of events generally accepted as belonging to the 

 process of fertilization, for in most organisms nuclear fusion 

 occurs in the same cell where nuclear association takes 

 place. It is generally conceded that before the haploid con- 

 dition of the nucleus is again established important pro- 

 cesses take place which we call reduction phenomena, the 

 full significance of which we perhaps are as yet ignorant 



of 



These 



including synapsis, cannot tat 

 has occurred, and some student 



place 



1 Just how the doubling arose in this instance is of course difficult to 



determine. Stomps ('12) suggested that it arose through the union of two 



unreduced diploid gametes, while Gates ('09, '13) thinks it arose through "sus- 

 pended mitosis of a megaspore mother cell" having (4x) 28 chromosomes, and 



its apogamous development. 



