10 



PRACTICAL BOTANY 



position, and a mass of distended cells pressing against one 

 another makes the whole structure rigid. But as when the air 



FIG. 7. A photograph of a cottonwood leaf from which the green tissue has 



been removed so as to show the network of veins through which the food 



material is carried throughout the leaf and to the stem 



Natural size. Leaf prepared by Ellsworth Bethel 



escapes from a balloon its wall collapses of its own weight, 

 so do the cells of the leaves and shoots when, through loss 

 of water, they lose their turgidity. When soil water is not 



