ZYGNEMACEE. 99 
var. b, Aquaticum. 
Zygogonium didymum, Rabh. Hedw. 1, t. 3, f. 2. 
Zygogonium Agardhii, Rabh. Alg. Eur. iii., p. 253. 
Conferva purpurascens, Carm. Eng. Fl. v. 350. Harv. Man. 
123. Mack. Hib, 224, 
In pools, bogs, &c. 
This is a very polymorphous species, some of the forms being terres- 
trial, and always sterile, others are aquatic producing zygospores. The 
old name of Zygogonium erictorum has been retained, but undoubtedly 
all these various forms belong to Zygogonium Agardhit, Rabh. (Zyg- 
didymum, RB.) 
“The colour, no less than the condition of the endochrome, varies 
considerably in this species. In some specimens the filaments are of a 
bright green, in which case they have always been found immersed in 
water; while in others, and more frequently, they are purple, of which 
aii they invariably are when found spreading over swampy heaths.” 
—Hass. 
Plate XL. fig. 2. Terrestrial form, a, sterile cells X 400 Fig. 3. 
var. aquaticum. a, sterile cells X 400; 5, ¢c, conjugating cells with 
zygospores X 400. 
Doubtful Species. 
Zygogonium gracile. Berk. 
Sterile cells about five times as long as broad, of a pale or 
yellowish green colour. 
Zygospore unknown. 
Siz. Cells -014.--016 mm, diam. 
Rabh. Alg. Eur. iii., 255. 
Zygnema gracile, Berk. Glean. t. 12, f. 8, 
Face of a dripping rock. 
Rabenhorst includes this with uncertain species of Zygogonium, but it 
seems more probable that it is a Zygnema, and perhaps one of the 
varieties of Z. Vaucherti. The following is the original description :— 
“Pale dirty yellowish green, mucous; threads extremely fine, articula- 
tions not at all constant in length, 4 to 8 times as long as broad, marked 
in the centre with two approximate roundish globules. Slender fila- 
ments occur in the same mass, with joints longer in proportion, the 
green mass not divided into two distinct portions. I have not seen it 
conjugated.’”’—Berkeley. 
Plate XL. fig. 4. Sterile cells X 400. 
Genus 48. MOUGEOTIA. De Bary. (1858.) 
Cells with axile chlorophyll-plates. Copulation ladder-like. 
Zygospore drawn together in the swollen, bladdery, persisting 
middle space. 
De Bary includes this genus in Zygnemee, although Wittrock joins it 
with Mesocarpus, and it seems to us very difficult to indicate any true 
generic distinction apart from the dividing off from the parent cells of 
the empty persistent cells which remain some time attached to the zygo- 
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