CHAPTER X. 



HOW PLANTS GROW. 



MUCH of the following is taken from a pamphlet by W. S. 

 Powell, of Baltimore, Md., and will no doubt be read with 

 interest. 



The Air. The air we breathe is a compound of gases. We 

 cannot see the air, but we can feel it when we move our hand 

 swiftly about, and we can observe its power when it is in motion 

 and is called wind. 



The air is a fluid which surrounds us on every hand, and it 

 has a very important part in the growth of crops and the life of 

 all plants and animals. Air is found to be made up of the union 

 of two invisible gases, called oxygen and nitrogen. It has also, 

 at times, other things mixed with it, but not a part of it, such 

 as water, in an invisible vapor, and other gases. Without air 

 no animal or plant can live. Growing plants take from the air 

 poisonous gases which animals throw off from their bodies, and 

 give back to the air what animals need for their good. So 

 we see that the air is the means of keeping both animal and 

 vegetable life on the earth. Animals in breathing the air use 

 up the oxygen gas, and throw off a poisonous gas, called car- 

 bonic acid, while plants take up this carbonic acid, which is 

 carbon and oxygen, use the carbon and reject the oxygen. 



Water. Water is composed of two gases, oxygen and hydro- 

 gen, in the proportion of one part of the former to two of the 

 latter ; it composes four-fifths of the flesh and blood of man, 

 and he uses three-fourths of a ton of it annually. Rain, which 

 is an essential of all crops and of all vegetables, is produced by 

 the evaporation of water in whatever form it may exist, from 

 the land, animals, and plants ; in this form it constitutes an in- 

 visible vapor that is taken up by the atoms in the atmosphere. 

 The property of all air is to rise when heated ; hence, whenever 

 air at any place becomes heated by decomposition of any sub- 

 stances, whether in the soil or on its surface, or from the heat 

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