ECOLOGY 



202. Subterranean stems and reserve food stores generally 

 ire devices for tiding over unfavorable seasons and permitting 

 the plant to make the best of a short growing season. The 



FIG. 42. Cassia, the wild sensitive pea. 



mnual and biennial plant habits are also evidently adaptations 

 :o seasonal changes, whether of temperature or moisture. 



203. The usual fall of temperature at night, which is often 

 rery considerable, is a condition to which some plants apparently 



