70 



Plant Physiology 



tissue or organ results in flaccidity or wilting. In Figure 

 19 are shown two lettuce plants transferred from soil. 

 The roots of plant A were put into water, and those of B 

 into 2.9 per cent sodium chlorid (approximately .5 gram- 

 molecular). The latter has caused a prompt loss of 

 water by the plant, so that wilting has resulted. 



If slices of beet or potato are placed in solutions similar 

 to those just mentioned, turgescence on the one hand and 



FIG. 20. Successive stages in plasmolysis : epidermis of Tradescantia 

 (a) and cells of Spirogyra (6). 



flaccidity on the other will result in the same manner. 

 The phenomenon of plasmolysis in the cell is sufficiently 

 important to be carefully studied. It is often more readily 

 observed in a cell with colored contents, or numerous 

 chloroplasts, so that the cells of filamentous algae, the 

 colored epidermis of certain begonias, or of Tradescantia 

 zebrina, also the stamen hairs of Tradescantia and Ana- 

 gallis, are convenient materials for demonstration. Figure 

 20 shows successive stages in the plasmolysis of the epi- 

 dermal cell of Tradescantia zebrina and of Spirogyra. 

 The concentration which will just cause the least trace of 



