244 ELEMENTARY SCIENCE 



plants in the world, and you can begin to understand their 

 various forms. For you know that all green plants are 

 trying to do the same thing. They are trying to relate 

 their root-hairs favorably to soil-water, and their leaves 

 favorably to light and air. All of the plant that lies be- 

 tween root-hairs at one end and leaves at the other simply 

 helps in getting these two things in good positions for 

 their work. The deep-burrowing roots of trees are neces- 

 sary to anchor the trunk and branches, as well as to reach 

 unfailing supplies of water, and the trunk and branches 

 are to get the leaves high in the air where they will not 

 be overshadowed by other plants. 



Leaves. What happens in the leaves ? Surely we 

 should understand this. Through all but the winter 

 months, the leaves of plants cover all the land, save where 

 man has cleared them away, or where there is not enough 

 water for plants to grow. They are so common, so beauti- 

 ful, and so important to us that every one should under- 

 stand their relation to our own lives, and the way in which 

 they do their work. The skin of a leaf may be very harsh 

 and tough, but inside it is always soft and tender. It is 

 filled with a soft green pulp. This soft pulp is made up 

 of many very small structures called cells. The bodies of 

 all living things are made up of cells which exist in many 

 forms and sizes. In this spongy, soft interior of a leaf the 

 great work of food-making goes on. Three things are 

 necessary to this work of food-making: (i) Sunlight is 

 necessary, for it furnishes the energy used in this work. 

 (2) Air is necessary, for it furnishes carbon dioxide, a sub- 

 stance used in the making of food. (3) Water is necessary, 

 because it, too, furnishes materials that are used in foods. 



