BOOTS AND THEIR RELATION TO PLANTS 23 



is called turgidity. Turgor doubtless helps to force water up- 

 ward through the stem. The distention of cells due to turgor 

 also accounts for the rigid or erect position of most leaves, 

 growing shoots, and succulent stems. Each distended cell, like 

 an inflated balloon, assumes a semi-rigid position, and a mass of 

 distended cells pressing against one another makes the whole 



FIG. 17. A young cucumber plant (grown in a flowerpot) 



At left, in normal condition ; at right, much wilted from having been left 

 unwatered for several days 



structure rigid. But just as, when the air escapes from a balloon, 

 its wall collapses of its own weight, so the cells of the leaves and 

 shoots collapse when, on account of loss of water, they lose 

 their turgidity. When soil water is not available to the plant, 

 the outgo from the leaves is often greater than the income from 

 the roots, and in such cases wilting follows (fig. 17). If water 

 does not again become available, the plant will die, but with a 

 renewed supply turgidity and the resulting rigidity soon return. 



