NEEDS OF ROOTS 31 



the roots carefully. It will he verj' hard to remove all the 

 fine particles of soil from these root hairs, so closely do they 

 cUng. These root hairs will be found along only a few inches 

 of the growing portion of the root just behind the root cap. 



29. Roots Take in Water. It has already been stated 

 tliat the leaves of plants give off water by transpiration. 

 Naturally, there must^be some source of supply from which 

 this water is drawn and some means of conveying it to the 

 leaves. The source of suppl}^ is the moisture in the soil; 

 it is taken in through the roots, whence it passes through the 

 stem to the leaves. The inner bark of the root and the stem 

 is made up largely of hollow cells placed end to end, which 

 make a ready means of passage for this water, or sap, as it is 

 ordinarily called after it is taken in by the plant. A shortage 

 in the supply of soil moisture is soon evident from the wilting 

 which takes place when water is given off more rapidly than 

 it can be taken in by the roots. Plants cannot draw all 

 the water from the soil. Clay soils will retain more than 

 sandy soils. It is easy to see that a reduction of the root sur- 

 face lessens the supply of water which the plant can obtain, 

 hence cultivating corn so deep that some of the roots are cut 

 causes the plants to wilt and checks their growth. The 

 gardener removes part of the leaves from his plants and 

 prunes his trees in transplanting them so as to reduce trans- 

 piration and lessen the danger from wilting, for he knows 

 that part of the roots have been broken off and those that 

 remain cannot supply enough water for the full leaf surface. 



30. Roots Require Air. As with all other hving parts of 

 the plant, the roots are constantly taking in oxygen and giv- 

 ing off carbon dioxide; that is, the process of respiration is in 

 progress. Consequently, roots require air. Most plants 

 cannot grow in a soil that is so filled with moisture that air 

 is largely excluded, though a few plants have become adapted 

 to this condition. Plants do not root deeply when there is 

 an oversupply of moisture, for it is not necessary for them to 



