Trow . — The K ary o logy of Saprolegnia . 643 
examination of the antheridium in Fig. 10 b. The apparent 
karyokinetic figures are produced by the stained granules on 
the nuclear wall at the time the nucleus is undergoing division, 
and the dark-coloured spindle is the nucleo-hyaloplasm. The 
chromosome-rods, already half the size of the original mass, 
are frequently at this time only distinguishable with difficulty 
from the larger granules. 
May not the figures of Wager be explained in the same 
way ? If the resting nucleus has really a single chromosome, 
as the figure of the gonidium seems to indicate, this must be 
regarded as very probable ; and should it be so, we might 
expect the karyology of the two genera to agree very closely. 
So much has this view appealed to me that I have already 
commenced an examination of Cystopus Candidas with a view 
of putting it to the test, and have secured material for the 
study of Peronospora parasitica. 
The evidence for the occurrence of fusions of nuclei 
in the unfertilized egg of Peronospora is extremely weak. 
Indeed, Wager’s figures suggest to me that no such fusion 
occurs. 
In the theory of heredity propounded so brilliantly by 
Weismann, the admixture of the substance which is the 
bearer of the hereditary tendencies during the sexual process 
is looked upon as the chief cause of variation in the higher 
organisms. An apogamous group, such as the Saprolegnieae 
was supposed to be, offers a special difficulty to the acceptance 
of this theory by botanists. The difficulty, however, is not 
a real one, as Weismann expressly rejects Nageli’s view that 
protoplasm has an inherent tendency to vary along certain defi- 
nite lines of development, and, consequently, he is of necessity 
driven to adopt the view that it varies under the direct influence 
of the external conditions. The sexual process becomes 
specially important in those organisms in which the gametes 
are protected by their position from the direct action of the 
external conditions. Such apocytial plants as the Sapro- 
legnieae, however, have their gametangia as much exposed 
to this direct action as the mycelium or zoospores, and the 
