24 THE VEGETATIVE FUNCTIONS OF PLANTS 



Some plants wilt much more readily than others, but in all 

 cases the wilting is due to the fact that water is being 

 continually given off by the plant. This may be easily 

 demonstrated by placing a living plant, or a few fresh 



FIG. 14. Aster sp., showing transition from petiolate, through petio- 

 late-stipulate, to sessile leaves. Note the elongation of the lower petioles, 

 thus bringing the blade out to better light exposure. 



leaves of any convenient plant, under a bell-jar or a 

 tumbler, whose inner surface is first known to be per- 

 fectly dry. As a check or control on the experiment a 

 second bell-jar should be placed beside the first one, but 

 without any plant or leaves under it. The inner surface 



