60 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 will 
soon die. The reason is now obvious. 
58. 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, 
^ 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. 
