1915] 



ATKINSON PHYLOGENY IN THE ASCOMYCETES 351 



ceive the long septate trichogyne of the highly specialized 

 Collema to be derived directly from the simple trichogyne of 

 the red algae, and then degenerate to the simple gamete of 

 lower more generalized Ascomycetes. 



NOTE V 



MODIFICATION OF SEXUAL PROCESS ALONG WITH STEEILITT OR LOSS OF THE 

 ANTHERIDIUM AND STERILIZATION OF THE ABCHICARP 



Sterility or loss of the antheridium. — Several species are 

 known in which the antheridium, though present, does not 

 function. In such cases sexuality is modified in such a way 

 that sex differentiation occurs among the nuclei in the as- 

 cogonium or in the ascogenous hyphae. Several examples 

 may be cited as follows: In Pyronema confluens (Brown, 

 W. H., '09) the antheridium sometimes fuses with the 

 trichogyne but there is no migration of its nuclei; in other 

 cases it may not connect with the trichogyne. The antheridial 

 nuclei degenerate. In still other cases the antheridium is ab- 

 sent. In Lachnea stercorea the antheridium fuses with the 

 terminal cell of the archicarp but its nuclei degenerate 

 (Fraser, '07). In Aspergillus herhariorum (Fraser and 

 Chambers, '07) and A. repens (Dale, '09) a similar situation 

 exists. In those numerous examples where spermatia (mostly 

 free *'antheridia") are present it is very likely that the sperm 

 nuclei no longer play a role in fecundation due to such exten- 

 sive sterilization of the terminal segments of the archicarp, 

 but the cytology of only a few species has been determined. 

 They no longer perform the function of fecundation in Poly- 

 stigma ruhrum (Blackman and Welsford, '12; Nienburg, '14), 

 Gnomonia erythrostoma (Brooks, '10), and in Collema pul- 

 posum (Bachmann, '13) the sperm nucleus has not been 

 traced through the long succession of sterile segments of the 

 archicarp, and it is very probable that it does not reach the 

 ascogonial cells. The spermatia are entirely absent in a num- 

 ber of species where archicarps are present, as in Laboul- 

 henia chaetophora (Thaxter, '96; Faull, '12). 



Sterilisation of the terminal portion of the archicarp and 

 differentiation of sex nuclei in the ascogonium or ascogenous 



