PLAXT SOCIETIES 



393 



peculiar in moving quickly. Tendrils curve undei the 

 influence of the same stimulus, but they move slowly. 



Light and darkness arc universal stimuli. Flowering 

 plants move toward the Light, it" it docs nol surround them 

 evenly on all sides. Window-growing plants Bhow this. 

 Plants like potatoes, which sprout in a cellar, grow many 



Figure 430. — Waterlilies — Hydrophytes. 



feet to get into the light. Darkness causes plants like 

 clover and oxalis to close their Leaves. 



Moisture is a stimulus which affects the roots of a plant, 

 as is shown in Figure 428. 



275. Plant Societies. — The term plant society is applied 

 to any collection of plants which grow under similar con- 

 ditions. The trees of the forests, and thegrass and weeds 

 of our lawns, are typical example-. In mosl cases water, 

 or the lack of it, is the basis \'^r classifying or grouping 

 plants in societ ies. Plants, Like some alga*. Live submerged 

 in the water, while others. Like the waterlilies. Live 



