THE RELATION OP THE PLANT TO WATER 155 



Water as a Food. — ^Water is frequently referred to as a plant 

 food. It is not a true food, but a crude or raw food that is abso- 

 lutely necessary for the existence of life. It is the most abun- 

 dant compound found in the plant. It is used not only in the 

 manufacture of true foods, such as starch and stigar (see page 

 195), but it also acts as a solvent in which the mineral salts 

 are dissolved before being absorbed by the plant. 



Location of Plant with Reference to Water. — The great im- 

 portance of water in the life and growth of the plant makes it neo- 

 essary that the plant must be so located as to secure the water to 

 the best advantage. Some plants, such as the pond weeds and 

 Algae, live more or less completely submerged in the water and 

 may be either free floating or attached ; other plants are anchored 

 in the soil and are either floating (pond lilies) or erect (cat- 

 tails) ; other plants live in swamps or wet soil, while the so-called 

 dry land plants live in soil which must contain some water in 

 order to support living plants. Therefore, it will be readily seen 

 that the character of the vegetation in any locality, large or small, 

 will depend largely upon the amount and distribution of the 

 water supply. Although water is necessary for plant growth, an 

 excess of water is injurious to many of our land plants. This is 

 very evident in young com during a period of excessive rainfall. 

 It is largely due to the fact that the excess of water in the soil 

 prevents the proper aeration of the root system (page 219). 



Methods of Absorption. — Some of the lower forms of plants, 

 especially the AlgEe, take in water through any part of their 

 surface, but the higher plants, including our agricultural crop 

 plants, take in practically all of their water through their root 

 systems. This is very evident when we take into consideration 

 the character of the. epidermal structures of the various parts 



