i 



FLINT FOOD AND GROWTH. 25 



gredients are taken up in solution, almost always in 

 a very weak solution. Roots also have the power of 

 dissolving some solid substances in the soil, such as 

 potash or phosphorus, and then absorbing them. This 

 action probably depends upon the acid sap in the 

 roots. Roots take up oxygen gas and also nitrogen, 

 when this is found in certain chemical combinations. 



The power of absorption by roots is believed to 

 be confined to a small space nearly at their tips; the 

 extreme tip being covered with a "root cap" of solid 

 dead matter. The large part of the roots have im- 

 portant uses, but not as food gatherers. 



The stem and its branches connect the roots and 

 leaves, carrying the water and dissolved solids taken 

 up by the roots to the leaves. 



The leaves are often called the lungs of plants. 

 Their action in relation to air is not, however, the 

 same as that of animals in breathing, either in man- 

 ner or effect. Animals inspire the air and give it 

 back charged with carbonic acid. Plants do the same 

 to a considerable extent. But plants, also have an- 

 other and most important power, entirely unlike any- 

 thing possessed by animals. The leaves especially 

 have the power of taking in carbonic acid and other 

 gases from the air. The carbonic acid is decomposed, 

 the oxygen given back to the air, the carbon being re- 

 tained and used by the plant. Starch is first formed 

 from the carbon and water. This is changed 

 into sugar, which is carried in the sap to different 

 parts of the plant and used to build them up. It is 

 hard to understand just how this is done, but it is 

 probably the most simple of the several processes 

 necessary to the building up of the plant which are 

 carried on by means of the leaves. 



