1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 347 



might under favorable conditions be the starting point of a 

 new ontogeny which would be similar to certain mutants. The 

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

 Oe. Lamarchiana with double the number of chromosomes is 

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

 '13), the diploid gametophyte and tetraploid sporophyte of the 

 mosses 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 

 example. But the normal expectation is that it would have 

 afterward a nuclear history in its ontogeny similar to others 

 with one nuclear fusion and one reduction from 2x to Ix. But 

 it is not likely that the entire group of sac fungi is founded 

 on such a mutation, followed by a double reduction with triple 

 division and then double fertilization again and so on. The 

 several cases where it has been quite well established that 

 there is no nuclear fusion prior to the ascus, together with 

 the great uniformity of the ascus nuclear phenomena in the 

 group, controverts the idea of any such origin for the sac 

 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 processes, including synapsis, cannot take place 

 unless nuclear fusion has occurred, and some students see in 



^ Just how the doubling arose in this instance is of course diflScult 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. 



