Adaptation to Environment. 



325 



side where they would become stopped up by the water, 

 even in the case of the taller leaves in the time of high 

 water. The upper surface of the leaf is coated with wax, 

 so that the water which 

 falls upon it rolls off with- 

 out wetting it and stop- 

 ping up the ways through 

 the stomata. The inter- 

 cellular spaces in the leaf 

 are large and numerous 

 and communicate with 

 tubular spaces in the ribs 

 of the leaf which are con- 

 tinuous with still larger 

 spaces in the petioles, 

 horizontal stems, roots, 

 and tubers. The sub- 

 merged parts are thus in 

 free communication with 

 the atmosphere. 



If we examine roots 

 which have been carefully 

 dug up, we find that they 

 extend but a short dis- 

 tance beneath the mud ; 

 indeed, the water-conduct- 

 ing and absorbing ele- 

 ments throughout the 

 whole plant are very 

 small compared with those found in xerophytes or even in 

 mesophytes. 



Thus we see that where water can be had without stint, 

 no special provision is made for its absorption, conduction, 



Fig. 174. 



Ranunculus fluitans. The lower figure shows 

 the land form and the upper figure the water 

 form, % natural size. After SCHIMPER. 



