258 BOTANICAL GAZETTE focihaak 
structures as conjugation tubes (Pyronema), accompanying sterile 
cells (Monascus), or an investing cellular envelope (Araiospora) 
might give rise to more conspicuous accessory structures. 
It need not be supposed that coenogametes of the second class are 
all derived from those of the first class, and in some regions there are 
good reasons for believing that this has not been the case, especially 
since the processes of oogenesis in Vaucheria (Davis ’o4) conform 
in the most essential features with those of the Peronosporales and 
Saprolegniales. These three groups agree inthe fundamental fact 
that extensive nuclear degeneration takes place in the gametocysis 
previous to the formation of the sexual cells. In Vaucheria all but 
one of the nuclei become disorganized. In Saprolegnia a number 
survive in relation to several coenocentra that determine the position 
of the eggs which are occasionally bi- and trinucleate. In the Pero 
nosporales the surviving nuclei lie in the ooplasm, and when only 
one is selected it is because of close proximity to the large coenocel 
trum. These conditions in the Peronosporales and Saprolegniales 
are so similar to one another and to Vaucheria in various particulars 
that there are evident relationships, but whether these are dined 
more general by way of a common ancestry among the lower Siphon- 
ales is a problem that perhaps may be better handled when we know 
more clearly the processes of oogenesis in such forms as Sphaeroples 
Monoblepharis, and some other types. Their processes of oogeness 
are likely t f in Vaucheria. 
e likely to conform to the type in Vau ypes of coeno> 
Whatever may have been the origins of the several t cae 
gametes representing the second class, problems which yee 
difficult and perhaps impossible to solve with the fragmentary ni of 
left to us, we can at least attempt to judge the probable men 
their development, and possibly establish some system OT 2 sat 
sexual evolution. As stated before, some botanists will bs 
even the simplest forms of coenogametes (Mucorales and are 
cales) have been derived from heterogamous algae by ‘eee 
plification or degeneration. The author cannot take pe seit 
believing as he does that the simplest coenogametes me i 
origin from isogamous algae, that they may tend to pass much the 
conditions leading to those of heterogamy, and that bse jn thi 
same factors are at work to differentiate the sexual eleme 
region of the plant kingdom as among the algae. 
