Trow.— The K ary o logy of Saprolegnia . 631 
When the oospheres are fully formed, we find, as represented 
in Fig. 15, that the nucleus still persists, but has undergone 
slight modification — the chromosome-mass has become more 
or less irregular. This irregularity of the chromosome left me 
for a long time in doubt as to whether fusions might not 
actually take place in the case of the functional nuclei at 
a very late stage, and I was especially anxious to determine 
this point in the apogamous forms. I have at last convinced 
myself that from the inception of the oogonium to the complete 
development of the oospheres, no fusion of functional nuclei 
takes place . 
Figs. 16 and 17 show clearly that both young and mature 
oospheres of 6*. dioica are uninucleate, and the small size 
of the nuclei and general behaviour leave no doubt in my 
mind of the occurrence of reducing divisions in this species 
also. Similar evidence may be brought forward with respect 
to the apogamous oogonia of S'. Thureti and S’, mixta. 
I cannot but conclude, however, that these observations will 
meet with considerable adverse comment, and it will be as 
well to bring forward at this stage additional independent 
evidence in support of them. 
Hartog, who admits that divisions take place in the 
antheridia, denies that they take place in the oogonia. All 
observers are agreed that the oogonia and antheridia are 
homologous organs. They represent the culminating point 
of a development, which, starting with typical isogamy, 
terminates in complete heterogamy. Such developments are 
obviously of secondary importance, but reducing divisions 
must be of primary value, as they of necessity date back to 
the evolution of the sexual condition itself. If the nuclei 
of the antheridia undergo division, it is extremely improbable 
a priori that the nuclei of the oogonia should remain 
undivided. 
Wager (’ 89 ) has carefully investigated the karyology of 
Peronospora parasitica , and has described and illustrated with 
numerous figures a process of karyokinesis which, while 
taking place in most parts of the plant, is particularly well 
