56 Fruit-growing in Arid Regions 



substances, injury to the plant may result. The presence 

 of free water for any great length of time deprives the roots 

 of the normal supply of air and results in death. Soil is 

 said to contain free water when the spaces between the 

 soil particles are filled. 



Soil water is taken up by the root-hairs by a process 

 known as osmosis. This process may be explained briefly 

 as follows: When two liquids, one concentrated and the 

 other dilute, are separated from each other by a thin mem- 

 brane, there will be a movement of the dilute solution 

 through the membrane into the more concentrated. This 

 is the only way that water can enter roots. The cell 

 contents of the root-hairs being more concentrated than 

 the soil solutions, the passage is into the plant. Should 

 the soil solutions by any means have the greater concen- 

 tration, the movement would be from the root-hairs into 

 the soil, and injury or death would result. This is what is 

 supposed to happen in those rather rare instances when 

 plants are injured by alkali. The soil water dissolves 

 these salts, and thus becomes more highly concentrated 

 than the cell contents of the root-hairs. 



From the root-hairs the moisture moves to the central 

 part of the root and on up to the stem. 



The Stem 



Did the reader ever stop to think of what use stems are 

 to plants, or why they have stems or trunks at all? We 

 know there are various forms of stems, ranging in size 

 from the smallest plant to the tallest tree. Some are thick, 

 others thin, and some, as the vines, require support. 

 Why all these various forms, and what, indeed, is the need 



