The Conjugation of Zygogonium ericetorum Kiitz. 243 
sometimes a few small oil globules, but no nucleus. 1 In the fact 
that the entire protoplast is not used up in the formation of the 
gamete Zygogonium ericetorum differs from Zygnema , but resembles 
Pyxispora and also Mougeotia (see discussion below). 
The curved wall which cuts off the gametangium is rather 
thin, and gives the usual reaction for cellulose. It is generally 
very convex, sometimes almost hemispherical, while it projects a 
variable distance into the lumen of the sterile cell—sometimes 
half-way across the latter. Very rarely is it almost plane. Although 
the two apposed gametangia were observed to be cut off generally 
at about the same time, yet in several instances one was seen to 
have been formed, while the corresponding cell in the adjacent 
filament had only just put out a slight protuberance, its chloroplast 
also being as yet unmodified (see Fig. 1, B); usually, however, the 
two conjugating cells were in about the same stage of devlopment 
The two gametangia were always approximately of the same size. 
At this stage the two gametangia, although organically inde¬ 
pendent, are firmly united, and rather violent treatment is 
required in order to separate them, although it is often done 
when teazing filaments apart for mounting. The binding mucilage 
often forms a conspicuous thick ring round the junction of the two 
gametangia, as mentioned and figured by de Bary, and as shown in 
Fig. 1, A, B. This gametangium stage seems to persist for some 
time, since it was rather frequently met with in conjugating fila¬ 
ments; in fact the whole process of zygospore-formation in this 
alga takes place remarkably slowly, and must occupy some 
considerable time. 
De Bary states that the separating-walls between the two 
gametes become gradually absorbed from the middle outwards, 
while the gametes fuse to form the zygospore. The Wyre Forest 
specimens, however, showed a stage, prior to fusion of the gametes, 
which is not mentioned by de Bary. This is the formation of a 
thin wall entirely surrounding each gamete (Fig. 1, C, a, and 2, 
A, a), and independent both of the partition-wall, which first cut 
off the gametangium, and of the wall of the protuberance of the 
conjugating-cell, although generally closely applied to both of these. 
This inner wall is thin and firm, is of cellulose, and easily recognised 
on account of its sharp contour, at any rate towards the distal end 
1 The material was not sufficiently abundant to enable the cytology of the 
process to be followed by appropriate staining methods. The nucleus pre¬ 
sumably remains in close association with the chloroplast. 
