ALGAE. — CONJUGA TAB 



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 fres-h-water Algae. 



De Bary distinguishes the following families :— 



I. The Mesocarpear consist of cylindrical cell-filaments with an axiie chl()ro|)liy]l- 

 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 obxiously 

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



n_5 



Fig. 25. FIG. 26. 



Fig. 25. Spirogyra tongata. On the left, cells of two filaments preparing- for conjugation ; they show the spiral chlorophyll-1 



each cell is surroundctl 

 of conjugatinsj ; at 

 ited ; in B the yoinig zygospor 



with grains of starch disposed here and there in them in rings, and small drops of oil. The nucleu; 

 protoplasm, threads of which pass to the cell-wall. At b preparations for conjugation. A to the right 

 the protoplasm of one cell is just going over into the other, at b the two protoplasmic bodies have 

 are already invested with a cell-wall. 



Fig. 26. A cell of Zygnema crticiatum with two stellate chlorophyll-corpuscles united by a bridge of colourless protoplasm, m 

 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 Mesocarpus, Craterospermum, and Stattrospermiim 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 



[2] 



