THE LIFE OF A PLANT 71 



shiny with moisture, the plant will suffer. We can see why 

 if we take some freshly boiled water and some water from 

 the well or the faucet, in different tumblers. Then take two 

 rooted cuttings, or young plants, washing off all the earth. 

 Put one in each tumbler, but over the boiled water pour a 

 little sweet oil. The other plant will grow the better. For 

 in- the boiled water there is no air, and no air can get through 

 the oil. A plant suffers, then, if for any reason air cannot 

 get to its roots. Air cannot well get into soil that is full of 

 water ; and though the plant will grow, it will grow better if 

 the soil is moist rather than wet. 



We know now, therefore, under what conditions a plant 

 grows best, and why and how it grows. The course of its 

 growth is simple. The main root grows longer, and usually 

 it branches, sending out threads in all directions. The stem 

 lengthens also, makes leaves, and usually also branches. 

 Through the membranes of the roots enters a solution of 

 plant foods, which passes upward to every part of the plant, 

 the water finally evaporating into the air. 



But if the root is very busy, so also is the leaf. To study 

 it properly we should need a real microscope ; it is work for 

 the higher grades. But the structure and the duty of the 

 leaf is easily explained. Each leaf is a factory of plant foods, 

 chiefly of starch. Through its surface it takes in a gas, 

 carbon dioxid. The oxygen of this gas it returns to the air ; 

 the carbon it keeps. Now the color of the leaf is caused by 

 many tiny cells containing a substance called chlorophyll. 

 This uses the sunlight, the carbon, and the materials supplied 

 by the roots, to make the food of the plant. A healthy 

 plant makes more food than it needs, and so is able to grow. 

 Indeed, it ought x to make more than enough to grow with, 

 so that it can store the starch in its tissues. 



It is this stored starch that enables a plant to flower. 



