59 DR. С. S. WEST ON THE ALGÆ OF 
The conjugating-tube is formed in the normal way and becomes very wide. 
During е fusion of the gametes the gametangia undergo a marked change. 
The terminal transverse walls increase greatly in thickness by the deposition 
of layer after layer of cellulose, and a slight thiekening of the side walls 
also occurs. Аз this thickening goes on the cavity of the gametangium is 
gradually reduced and a hemispherical, or sometimes a bluntly conical mound 
of cellulose projects into the emptying gametangium. The metamorphosis 
of the gametangium, which might almost be described as a “ solidification,” 
keeps pace with the receding of the gametes, and when the latter have 
completely coalesced in the wide conjugating-tube, the proximal ends of the 
four solid processes project as four rounded buttons into the cavity of the 
zygospore. The mature zygospore possesses four cylindrical truncate horns, 
each of which bas arisen without external change of form from one half of 
a gametangium, the latter having become solid by the deposition of an internal 
thickening of cellulose. 
I have pointed out on previous occasions the curious change which is 
undergone by the gametangia of species of Debarya during conjugation *. 
In D. desmidioides there are four solid processes to each zygospore formed 
in a similar way to those of D. Hardyi. In D. africana the thickening is 
considerable, and laid down evenly except for the terminal pits, but the 
gametangia do not become solid. 
The gradual acquirement of solidity by the erstwhile thin-walled gamet- 
angia of D. Hardyi is well shown in figs. 7-9, PI. 2. 
Genus ZYGNEMA, 4g. 
ll. ZYGNEMA spontaneum, Nordst. Alg. aq. dule. et Char. Sandvic. 1878, 
р. 17, t. 1. figs. 23-24 ; W. у. G. S. West, т Journ, Bot. 1897, p. 40 ; in 
Ann. Roy. Bot. Gardens, Calcutta, vi. (1907) p. 184.—2. Heydrichi, Schmidle, 
т Flora, Ixxxiv. (1897) р. 169, t. 5. figs. 5-7, 10, 11. 
Crass. cell. veget. 1575-17 р; diam. zygosp. 29-34 и; diam. aplanospor. 
20 u. (РІ. 2. figs. 2-3.) 
Hab. Yan Yean Reservoir, at the weedy margins (Nov. and Dec. 1905 ; 
Jan. 1906). 
In size and proportions, and also in the aplanospores, the Australian 
examples agreed almost exactly with those described by Nordstedt from the 
Sandwich Is., but the zygospores exhibited a considerable degree of variation 
in form and position. The zygospores previously observed from W. Africa 
and from Burma were entirely contained in the female gametangium, which 
was slightly swollen to accommodate the spore. In the Australian specimeus 
the zygospores were of relatively greater diameter, and that part of the 
ж W.& G. S. West in Journ. Bot., March 1903, p. 8; G. S. West, Treatise Brit. Freshw. 
Alg. 1904, p. 127 ; in Journ. Linn. Soc., Bot. xxxviii. (1907) p. 104. 
