115 



rounds. In each cell thus connected with another a single 

 large gamete is formed, and one of them passes through the 

 connecting tube to the other. The gametes are similar, and 

 their fusion results in a heavy- walled oospore (Fig. 104, D), 

 which endures through the winter and germinates during 

 the following season. ) 



Plasmolysis. Spirogyra is a very favorable form for 

 demonstrating plasmolysis, which means the shrinkage of 

 protoplasm .from loss of 

 water. The cytoplasm 

 of an active cell is full of 

 water, which often col- 

 lects in droplets of vary- 

 ing size, called vacuoles. 

 There is always a layer 



B 



FIG. 106. Plasmolysis: A, a cell of Spirogyra 

 before plasmolysis; B, the same cell after 

 plasmolysis with a ten per cent solution of 

 salt. 



of cytoplasm in close con- 

 tact with the cell-wall, 

 but the interior of the 

 cell may be one large 

 vacuole traversed by 

 strands of cytoplasm, as 

 in Spirogyra. The turgor of the cell ( 64) keeps the elastic 

 wall distended; but if the cell be put in a solution of sugar, 

 water will be withdrawn. The vacuoles thus beginning 

 to lose their water, the cytoplasm shrinks; and if the loss 

 continues, the vacuoles are obliterated, and the layer of 

 cytoplasm in contact with the wall separates from it, all 

 the cytoplasm of the cell contracting into a compact mass 

 (Fig. 106). The name plasmolysis really means the " loosen- 

 ing" of the "plasma" (protoplasm) from the wall. Any- 

 thing that withdraws water from a cell plasmolyzes it, and 

 the filamentous Algse are favorable forms for experiments 

 to^show this. 



70. Conclusions. The green Algae are so named because 

 the green of the chloroplasts is neither modified nor obscured 



