ALG 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 odspore (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 cellisfull of 4 
water, which often col- 
lects in droplets of vary- 
ing size, called vacuoles. = 
There is always a layer 
of cytoplasm in closecon- B 
tact with the cell-wall, 
but the interior of the 
ll i 1 Fic. 106.—Plasmolysis: A, a cell of Spirogyra 
ce. may e€ one large before plasmolysis; B, the same cell after 
vacuole’ traversed by plasmolysis with a ten per cent solution of 
strands of cytoplasm, as te 
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water will be withdrawn.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 Alge are favorable forms for experiments 
to show this. 
70. Conclusions.—The green Algz are so named because 
the green of the chloroplasts is neither modified nor obscured 
