PERSONALITY OF PLANTS 
Another substance which is always present in 
excess of plant needs is water. It is essential as 
a tissue builder and also as a carrier of nourish- 
ment. Its continual evaporation from the leaf 
surfaces furnishes one of the sources of motive 
power for the circulatory system. ‘The rate of 
evaporation is controlled by the stomata, little 
pores or mouths which have contractible lips. 
In the Lilac there are as many as one hundred 
and twenty thousand stomata to the square inch. 
They are nearly always located on the under sur- 
face of the leaves. 
Certain plants like the Cacti seem to be able 
to get along without leaves, but thick, fleshy 
sections of stem perform all their functions. The 
Fungi and other parasites differ from most 
plants in that they have no chlorophyll for 
starch-making but live on the already elabor- 
ated tissue of living or dead neighbors. 
When our seedling grows old enough, it mar- 
ries and has a family. Among the higher 
plants, the sexes are quite distinct. There are 
such things as male plants and such things as 
female plants, but more often both sexes oc- 
cur in the same individual and frequently in 
[34] 
