ALGAE. CONJUGA TAE. 



49 



becomes a zygospore, which germinates after resting for some time ; it differs essen- 

 tially in form from the vegetative cell. There are no brood-cells. All the' species of 

 this group are fresh-water Algae. 



De Bary distinguishes the following families : 



I. The MESOCARPEAE consist of cylindrical Cell-filaments with an axile chlorophyll- 

 plate, which as they lie parallel to one another either, put out conjugating processes 

 toward one another, or touch each other in spots where the filament is bent like a knee : 

 the walls at the point of contact being absorbed, a broad canal for conjugation is thus 

 formed, in which the protoplasm of the two conjugating cells collects ; and the space in 

 which conjugation is effected being shut off by the formation of two or four trans- 

 verse septa, its contents become a zygospore. This mode of formation obviously 

 recalls the similar proceeding in the case of the Zygomycetes. The germination of the 



FIG. 25. 



FIG. 25. Spirogyra longatct. On the left, cells of two filaments preparing for conjugation ; they show the spiral chloropyll-bands. 

 with grains of starch disposed here and there in them in rings, and small drops of oil. The nucleus in each cell is surrounded by 

 protoplasm, threads of which pass to the cell-wall. At b preparations for conjugation. A to the right in the act of conjugating ; at a. 

 the protoplasm of one cell is just going over into the other, at b the two protoplasmic bodies have united ; in B the young zygospores 

 are already invested with a cell-wall. 



FIG. 26. A cell of Zygnema cruciatum. with two stellate chlorophyll-corpuscles united by a bridge of colourless protoplasm, in 

 which lies the nucleus. 



zygospore produces directly a new cellular filament, in which the extremity that remains 

 in the spore is the base, and the free extremity the apex ; but this distinction is not 

 maintained, since all the cells are alike and multiply by growth and transverse division. 

 The genera Mesocarpits, Craterospermum^ and Staurospermum belong to this family. 



2. The ZYGNEMEAE also consist of cylindrical cellular filaments with straight or spiral 



parietal chlorophyll-bands or stellate chlorophyll-corpuscles in pairs (Fig. 26). In 



conjugation two filaments place themselves parallel with one another, and their cells put 



out processes toward one another (Fig. 25), which meet and by dissolution of the walls 



W E 



