638 Trow . — The Karyology of Saprolegnia. 
The oogonia may contain binucleate oospores alone, uni- 
nucleate oospores alone, or a mixture of these in various 
proportions. 
In 5. mixta then we conclude that fertilization frequently 
takes place, but in default of its occurrence the oosphere 
may develop parthenogenetically. The diclinous, andro- 
gynous, and completely apogamous forms investigated, thus 
form a very interesting series as regards sexual capacity : 
vS. dioica is typically sexual, S. Thureti is typically apoga- 
mous, and vS. mixta occupies an intermediate position. 
An examination of Humphrey’s figure of a binucleate 
oospore of Achlya americana , already referred to, leaves no 
room for doubt in my mind that a process of fertilization 
takes place in this species also. The figure of the uninucleate 
oospore — provided that the other nucleus has not been over- 
looked — leads me to believe that an apogamous development 
of the oosphere is also possible in this case. Humphrey’s 
view that these constitute the last pair of fusion-nuclei is 
manifestly incorrect. 
Hartog (’89), who appears to have investigated one or two 
other species of Achlya (either A. recurva or A. prolifer a , or 
both), agrees with Humphrey that the last fusions of the 
nuclei may be delayed in Achlya until the formation of the 
young oospore. This remark leads me to believe that 
a second (if not a third) species of Achlya at least undergoes 
occasional fertilization. The fact that Hartog did not find 
binucleate oospores in Saprolegnia may be traced most 
probably to an examination of apogamous forms like 
Thureti. 
It appears clear that not the least interesting of the results 
of this investigation is the discovery of a distinct and unequi- 
vocal process of fertilization in at least four species from 
a group which has for many years been almost universally 
regarded as affording one of the most interesting cases of 
complete apogamy . 
Maturation of the oospore. This was studied first in S. dioica 
by means of preparations stained with acetic carmine or 
