ALGJE 



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 

 of cytoplasm in close con- B 

 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 water will be withdrawn.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 Algae 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 



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

 before plasmolysis; B, the same cell after 

 plasmolysis with a ten per cent solution of 

 salt. 



