6o THE VEGETATIVE FUNCTIONS OF PLANTS 



simple manner by the well-known fact that, if a quantity 

 of salt is placed on the soil around a plant, the plant w^ill 

 soon die. The reason is now obvious. 



68. Rigidity. — Attention has been called to the fact 

 that water serves as the vehicle by which substances in 

 the soil are carried into the roots and transported to all 

 parts of the plant. But the water serves another use in 

 helping to keep the parts of the plant rigid, and thus main- 

 taining their form. This service is accomplished chiefly 

 by means of the osmotic pressure which obtains in every 

 individual cell. If every cell is turgid, tissues as a whole, 

 and the organs of which they form a part will be rigid. 

 This may be easily demonstrated by plasmolyzing the 

 cells in a piece of rigid plant tissue, and then restoring 

 their turgor. 



A fresh piece of a beet or turnip, about 2 inches long, 

 3.^ inch wide, and y^ inch thick will be found to be quite 

 rigid, so that it cannot be easily bent without breaking. 

 If the piece is now placed in a 5 per cent, solution of table 

 salt for 10 or 15 minutes or longer, it will be found to have 

 lost its rigidity, and may be bent nearly double without 

 breaking. The salt-solution as we know, caused the 

 plasmolysis, and consequent loss of turgor of every cell, 

 and so the entire tissue became flabby. 



