No. 460.] STUDIES ON PLANT CELL.— V. 251 
is substituted for the union of gamete nuclei but the phylogenetic 
and evolutionary aspects of sexuality are disregarded. Also, the 
nuclei that fuse are sometimes very closely related, which is a 
condition generally avoided in sexual processes except where 
peculiarities of habit make close inbreeding necessary. It is 
true that large groups, such as the Basidiomycetes, perhaps 
certain regions of the Ascomycetes, some Phycomycetes, and 
some forms of the higher plants and algae seem to have given up 
normal sexual processes but there is much evidence that in many 
cases this loss of sexuality is associated with a certain degree of 
segregation and with peculiarities of life conditions apart from 
the normal activities of all organisms or quite different from the 
ancestral stock. The groups are likely to be distinguished by 
highly specialized life habits of a sort that make it impossible 
for inherited sexual organs to function, either through mechan- 
ical difficulties or because one or both degenerate. It seems to 
me much clearer to regard all illustrations of Blackman's 
“reduced forms of fertilization" under the general term of 
apogamy even though it may be clear that they are physio- 
logical substitutes for sexual acts and to reserve the term fertil- 
ization for the union of gametes which can always be clearly 
identified through morphology in ontogeny and phylogeny. The 
success of a group even though ancestral sexual processes may 
be suppressed does not enter into a problem which is at bottom 
a morphological one. Success is relative and we really have no 
means of estimating its degree save by actual experiment. It is 
not likely that any biologist would claim that sexual degenera- 
tion is advantageous to any species although the organic world 
is full of forms which have dispensed with sexuality and still 
hold their places. These are the reasons why I have grouped 
cell unions and nuclear fusions as sexual and asexual on a mor- 
phological basis founded on phylogenetic principles and why in 
Section V, we shall devote some attention to the substitutes for 
sexuality under the head of apogamy. 
The Ascomycetes present a phenomenon of nuclear fusion 
within the ascus which may properly be considered at this time 
since there is a certain resemblance to the nuclear fusions in 
the teleutospore and basidium. Dangeard ('94—95b) gave the 
