2 4 
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 
