1904] DAVIS—SEXUAL.ORGANS IN PLANTS 257 
character under certain conditions, as through a change from aquatic 
to aerial habits, might give up the habit of developing motile sexual 
elements, which would be represented, however, by the numerous 
gamete nuclei fusing in pairs in the cytoplasmic union of the parent 
coenogametes. We have excellent illustrations of the sacrifice of 
motile spore-forming habits in the conidia of Peronospora and some 
species of Pythium, which germinate by a tube instead of developing 
zoospores. These conidia are morphologically sporocysts which 
have become coenocytic units, and coenogametes are gametocysts 
which have become coenocytic units. It must not be supposed that 
coenogametes are all related to one another. They might readily 
arise, according to our theory, from various types and at different 
times, thus making possible a number of developmental lines. 
The coenogametes of the second class are restricted portions of 
cells, which like those of the first class are morphologically gameto- 
cysts. Indeed in many cases the mother-cell is essentially a unit, 
even though only a part of the protoplasm is actually the sexual ele- 
rain because the remainder has some special relations or functions 
m connection with the sexual processes. Thus the periplasm of the 
Peronosporales and the conjugating tube of Pyronema hold such 
inimate relations to the sexual portion of the protoplasm that the 
‘aire gametocyst is really a coenocytic unit, and might be called the 
"a _ of the restricted portion that is actually fertilized. 
‘ian. 8 in the genus Albugo it would seem that some 
inc, we sig the second class follow the general law of sexual 
» Feducing the number of functional gamete nuclei until 
cae te The series from Albugo Bliti and A. 
apa a A. Tragopogonis to A. epee and A. Lepigont 
roe already —— ae and the author (Davis ’03), p. 323, 324) 
that the OSes Is agreement with STEVENS and RUHLAND 
order, from the wi opment in the genus is plainly in the above 
Wik ara ae ee to the uninucleate egg. We may hope 
cover Phe. veHES on the sexual organs of Ascomycetes to dis- 
insuffi-; ty lines in this group, but our knowledge is entirely 
“ent at present to justify conclusions. Thus, uninucleate 
fametes like those of Sph 7 : ; i 
Process of a... P aerotheca may represent the last stage in a 
reduction. And along a very different line such 
