270 GENERAL SCIENCE 



influence of the sunlight, carbon is built into the substances 

 starch and sugar. These are foods for the support of plant 

 growth as well as foodstuffs for animals. The liberated 

 oxygen is returned to the atmosphere. 



Carbon dioxide gas used by plants in making their food is 

 a product of the oxidation of substances containing carbon. 

 Its chief sources are the respired air of all forms of animal 

 life, the combustion of vegetable matter including coal, and 

 the decay of vegetation. The loss of the leaves of any 

 plant by hail storms, " worms," or caterpillars, deprives 

 the plant of power to produce enough food for its continued 

 growth after any stored supply has been exhausted. This 

 means a starved condition for the plant that is likely to kill it. 



Not least of the activities of the leaves of plants is their 

 liberation of water which has come up to them from the 

 depths of the soil through their roots. A single thrifty 

 sunflower plant gives off into the air by transpiration as 

 much as a quart of water per day. It has been estimated 

 that a large tree with abundant foliage may evaporate through 

 its leaves several barrels of water daily during the growing 

 season. From the grass of lawn and field the quantity 

 evaporated daily at times during the growing season may be 

 estimated as tons per acre. The loss of water from leaves 

 as well as the absorption of carbon dioxide from the air is 

 chiefly through the more open cellular tissue of the under 

 sides of the leaves. 



This would be a strange world in which to live if there 

 were none of the variety of landscape due to plants of all 

 sorts and kinds. When to the plants that are familiar to 

 us there are added the myriad forms of microscopic size of 

 which Botany teaches, and when we consider the usefulness 

 of bacteria as man is coming to know more and more about 

 them, studies of the plant kingdom assume an importance 

 far beyond any mere love of flowers for their beauty alone. 



