ZYGNEMACEJE. 99 



var. b, Aquaticum. 



Zygogonium didymum, Rabh. Hedw. 1, t. 3, f. 2. 

 Zygogonium Agardliii, Rabh. Alg. Eur. iii., p. 253. 

 Conferva purpurascens, Carm. Eng. Fl. v. 350. Haw. 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 foi ITS belong to Zygogonium Agardhii) Rabh. (Zyg- 

 didymum, R.) 



" 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 iu 

 water; while in others, and more frequently, they are purple, of which 

 colour they invariably are when found spreading over swampy heaths." 

 Hass. 



Plate XL. fy. 2. Terrestrial form. , sterile cells X 100 Fig. 3. 

 var. aquaticum. a, sterile cells X 400 ; b, 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. 

 SIZE. Cells -014.--016 mm. diam. 

 Rabh. Alg. Eur. iii., 255. 

 Zygnema gracile, Berk. Glean, t. 12, f. 3. 



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. Vauclierii. 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 Zygnemeos, 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- 



P 



