The Conjugation o/Zygogonium ericetorum Kiitz. 2^7 
jugation with one or more other filaments, while these lengths 
would be separated by intervals—of variable length—of purely 
vegetative cells. 
The four pyrenoids are sometimes recognisable in the young 
zygospore, and scattered starch-grains may also he present, but 
in the mature zygospore no pyrenoids are to be made out, and the 
reserve-material consists of large globules of a fatty oil, no starch 
being present. 
The formation of azygospores or parthenospores was observed 
in a few cases, but their occurrence must have been very rare. 
Three successive stages (from right to left) in the development 
of an azygospore are shown in Fig. 2, E, from which it is clearly 
seen that the gametangia never fuse, but that one becomes 
enlarged, its contents takes on a thick lamellated cell-wall, and 
forms the azygospore. The latter is smaller than the zygospore 
(being about 22-5 /j. long, and 15/x wide), but has the same densely 
granular contents, and numerous oil-globules; its shape is more 
or less ellipsoidal. The companion gametangium degenerates, and 
eventually becomes a mere shrunken appendage. Although not 
actually observed it seems quite possible that occasionally both 
the gametangia may develop simultaneously, without fusion, to 
form twin zygospores. 
A rather curious state of affairs is figured in Fig. 2, D, where 
four cells have conjugated crosswise, so that the resulting zygo¬ 
spores lie one above the other, and are crossed,although several other 
cells of the two filaments had conjugated normally. The crossed 
zygospores may possibly be explained by the four gametes concerned 
being so placed that each is directly opposite to one of its own 
“ sex ” (cf. above), while the diagonal pairs of gametes are of 
opposite “ sexes.” This, however, is only put forward as a 
suggestion, as the condition may be the result purely of accident. 
Two examples of germinating zygospore were seen, one of 
which is figured (Fig. 2, F). In both cases the zygospore had 
elongated and divided into two exactly similar cells, while the 
embryo filament had retained its connection, at one end, with 
one of the conjugating filaments, as shown. There is no differenta- 
tion into base and apex in the young filament. 
111. Conclusion. 
It seems clear that the above must be regarded as the 
normal method of conjugation of Zygogonium ericetorum . In what 
