256 BOTANICAL GAZETTE [october 
The Perisporiaceae, Lichenes, and Laboulbeniaceae among the 
Ascomycetes present sexual organs of a highly differentiated character. 
These are very much specialized groups whose morphology and life 
histories indicate a degree of development and differentiation far 
above most of the simpler forms that we have just discussed (Gym- 
noascus, Monascus, Pyronema). The gametes of Sphaerotheca 
(HARPER ’95, ’96) are uninucleate, and it becomes an interesting 
problem whether or not this form stands at the end of a series repre- 
senting nuclear reduction from a coenogamete, such a series as i 
illustrated by the species of Albugo. The recent studies of Baur 
(°98, ’o1) and DaRBISHIRE (’oo) on the lichens have clearly estab- 
lished the sexuality of these forms and the significance of the asco- 
genous hyphae. But we do not sufficiently know the nuclear conti- 
tions to justify any extended speculations on the homologies of the 
cells in the archicarp and trichogyne of the female sexual orga. 
And similarly the sexual organs of the Laboulbeniaceae (THAXTER 
’96) present most interesting and puzzling complications of cell 
structure that cannot be explained until we know the detailed history 
of the nuclei in the processes of development and fertilization. 
In a discussion of the origin and evolution of coenogametes much 
depends upon the relation of the structures in the first and 
class. Which is the more primitive type? Some botanists will 
‘claim that conditions of the first class (Mucorales and pas 
mycetes) illustrate degeneration from higher sexual forms. 7 
author is of an opposite opinion, believing that the ec | 
the first class illustrate closely the conditions of very simple ma 
most primitive types of coenogametes. This view has been di oi 
in a previous paper (Davis ’o03 6, pp. 233-3273 and 331-339) but 
be summarized briefly here. 
The a the first class are morphologically se 
cysts which have given up the function of forming senor “a 
(represented by the many nuclei), but obeying chemotactic re 
Ww 
and their progenitors would be looked for among grou eee 
gametocysts discharged motile gametes that fused 1m 
illustrated among the isogamous Siphonales. An ane 
* 
i 
