BEGINNERS' ZOOLOGY 



Energy in the Organic World. — We see animals exerting 

 energy; that is, we see them moving about and doing 

 work. Plants are never seen acting that way; yet they 

 need energy in order to form their tissues, grow, and raise 

 themselves in the air. 



Source of Plant Energy. — We notice that green plants 

 thrive only in the light, while animal growth is largely in- 

 dependent of light. In fact, in the salt mines of Poland 

 there are churches and villages below the ground, and 

 children are born, become adults, and live all their lives 

 below ground, without seeing the sun. (That these people 

 are not very strong is doubtless due more to want of fresh 

 air and other causes than to want of sunlight.) 



^ The need of plants for 



snnligJit shows that they 

 must obtain something 

 from tlie sun. This has 

 been found to be energy. 

 This enables them to lift 

 their stems in growth, and form the various structures 

 called tissues which make up their stems and leaves. 

 It is noticed that they take in 

 food and water from the soil 

 through their roots. Experiments 

 also show that green plants take 

 in through pores (Fig. 1), on the 

 surface of their leaves, a gas 

 composed of carbon and oxygen, 

 and called carbon dioxide. The 

 energy in the sunlight enables the 

 plant to separate out the carbon, 

 of the carbon dioxide and to build 

 mineral and water and carbon 



Fig. i. — Surfaces of a Leaf, 

 magnified. 



v Acid Gas 

 in the Air going 

 into the Leaf 



"Water 



Fig. 2. — A Leaf storing 

 Energy in Sunlight. 



