Water-Content of Plants 39 



reduced by several hundred per cent. This may go on 

 simultaneously with a reduction in the water-content of 

 the plant as a whole, which is the case in cereals and many 

 other plants having a definite growth cycle. On the other 

 hand, the maturity of the seed in many annuals and per- 

 ennials which grow in an indefinite manner may be wholly 

 independent of any general ripening process of the entire 

 plant. 



The seed within the body of the fruit may likewise differ 

 from the latter ; thus the seed of watermelon or peach 

 shows, when the fruit is ripe, a water-content far less than 

 that of the pulp which surrounds it. The water of the 

 plant does not merely permeate all parts indiscriminately ; 

 it is accumulated within or withheld from organs by virtue 

 of complex histological, chemical, or physical relations. 

 The formation of a few layers of corky tissue may cut off 

 the water-supply of an organ, the storage of solid food- 

 materials may reduce the quantity of water, or the pres- 

 ence of certain compounds may increase or inhibit absorp- 

 tion. 



28. The water-absorbing system. - The root-system 

 constitutes the mechanism whereby the water-supply 

 must be secured in practically all higher plants, including 

 the common agricultural plants. There is, moreover, 

 diversity in the form, texture, and distribution of the roots 

 of crop plants. The diversity in form and texture is not 

 necessarily coupled with great differences respecting the 

 water-supply furnished. 



There are two general types of root complexes ordinarily 

 recognized. In the one there may be a central or main 

 root called the tap-root, the branches and sub-branches 



