The Conjugation of Zygogonium ericetorum Kiitz. 245 
gamete of Fig. 1, D, b, where a somewhat later stage of fusion is 
figured. Thus at stages a and b (Fig. 1, D) there is a distinct 
morphological differentiation between the gametes ; but although 
always to be seen in the early stages of fusion, the distinction is 
lost in the stage figured in Fig. 1, D, c. It seems clear, there¬ 
fore, that there is a slight sexual difference between the two 
gametes, the one putting out the process being looked upon as 
male, the other as female. The cells of any particular filament, 
however, do not give rise exclusively to gametes of one “sex.” 1 
The ultimate product of fusion is a more or less ellipsoidal 
zygospore (Fig. 2, B) round which frequently an equatorial furrow 
often persists for some time but eventually disappears. The thin 
inner wall of each gametangium remains round the corresponding 
half of the zygote, the two membranes becoming fused together 
round the middle of the zygospore to form a perfectly continuous 
wall round the latter; and this investment persists as the outermost 
layer of the wall of the zygospore. It is quite clear that the thin inner 
walls of the gametangia do not become mucilaginous like the wall 
of the “conjugation-canal”; and that they persist throughout 
fusion of the gametes—only becoming absorbed locally in order 
that this can take place—and eventually join up to form the first 
membrane round the zygote. This membrane is undoubtedly added 
to as the slow fusion of the gametes proceeds, and, as the zygospore 
ripens, continuous layers are deposited internally, so that the wall 
of the mature zygospore is thick and lamellated, but remains 
colourless and smooth. 
The mature zygospore (Fig. 2, B, C) is 26-30/x long, 16-20 yu 
wide, subellipsoidal or subglobose, and resembles very closely, but 
is not quite so irregular as those of “ Zygnema pachydermum ” 
figured by W. & G. S. West (11). It is easily set free from the 
“ conjugation-canal ” since the latter becomes very mucilaginous, 
and sometimes almost disappears. When the zygospore is thus 
set free the septa, which first cut off the two gametangia, always 
remain behind attached to the cell-walls of their of their respective 
conjugating-cells (Fig. 2, A, C), and never become detached with 
the zygospore, 
The filaments generally conjugated in an irregular fashion 
3 or 4 often conjugating amongst themselves. It was always 
found that short lengths (of 1-10 cells) of a filament were in con- 
1 Cf. in this respect, “ the crossed zygospores ” described below. 
