ROOTS 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 
Fic. 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. 
