CHAPTER XII 



THE WATER OF THE SOIL IN ITS RELA- 

 TION TO PLANTS 



WATER, as has already been shown, is one of the external 

 factors in plant growth in that it is necessary in the 

 processes of weathering, which results in the simplifica- 

 tion of compounds for plant utilization. It also func- 

 tions as an internal factor in plant development, inasmuch 

 as it maintains the turgidity of the plant cells, acts as a 

 carrier of food materials, functions as a regulator, and 

 can actually be utilized as a source of hydrogen and 

 oxygen. These direct or indirect relations of water 

 to plant growth may be considered under three heads, 

 as follows : 



167. Relations of water to the plant. 



1. Water acts as a solvent and a carrier of plant-food 



materials. It is therefore a medium of transfer 

 for the mineral and gaseous elements from the 

 soil to their proper places within the plant. 



2. As a food water either becomes a part of the cell 



without change, or is broken down and its ele- 

 ments are utilized in new compounds. 



3. Water in maintaining turgidity, in equalizing the 



temperature by evaporation from the leaves, and 

 in facilitating quick shifts of food from one part 

 of the plant to another, acts as a regulator during 

 assimilation and while synthetic and metabolic 

 processes are going on. 



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