REVIEW OF PLANTS STUDIED 91 



3. Leaves. The leaves are as important to the life of plants 

 as roots. The largest amount of the food of plants is de- 

 rived from the air by means of the leaves. If a plant is 

 defoliated, it may reproduce a new set of leaves from re- 

 serve material stored in its tissue, but it is always injured 

 and produces little or no fruit. If defoliation is repeated, 

 the plant will die. Potato beetles and caterpillars often 

 kill plants by defoliation. Leaves, as also the stem and 

 branches, give beauty and characteristic forms to plants. 

 Try to recall a number of the different forms of leaves you 

 have observed. Leaves are nearly always more or less thin 

 and flat, like a piece of paper, because this shape enables 

 them to present the largest possible surface to the air. 

 You will not find leaves that are tuberous like a potato. 

 The leaf veins serve to keep the leaf spread out. In grasses 

 and lilies they run nearly parallel to one another, but in the 

 leaves of most of the plants that we have studied they form 

 a beautiful network. The venation is best seen if you hold 

 a fresh leaf between your eyes and the light. By far the 

 larger number of trees and shrubs in northern countries 

 shed their leaves in the fall. As the temperature of the 

 air in our winters remains below the freezing-point of water 

 for months at a time, the water in the leaves would ' freeze, 

 growth would be suspended, and the leaves would only fur- 

 nish a large surface for snow and storms. Our trees and 

 shrubs overcome this difficulty by producing a new foliage 

 in spring, and by shedding it when the season's growth has 

 ceased. 



4. Flowers. Those parts of a plant which are specially 

 adapted to the production of seed are called the flowers. 

 The essential parts of a flower are stamens and pistils. It 

 is necessary for the growth of seeds that pollen from the 

 anthers be transferred to the stigmas of the pistils. On the 



Are they all entitled to be treated wi 



