Water-Content of Plants 37 



stances to support a considerable load of branches, leaves, 

 and flowers. Any condition which deprives the plant of 

 water inaugurates, on the contrary, a state of flaccidity; 

 that is, a drooping or wilting. These phenomena will be 

 referred to again, but the fact may not be too strongly 

 emphasized that rigidity and abundant water-supply are 

 closely related, especially where the mechanical supporting 

 tissues do not reach the fullest development. Compare 

 the appearance and vigorous yield of well-watered lettuce, 

 squash, or tomatoes with those unattractive and miser- 

 able plants whose, leaves or fruits fall limp upon them- 

 selves. 



26. The water-content of plants. The growing plant 

 contains invariably a high percentage of water. It is gen- 

 erally stated that an active, succulent plant or tissue, one 

 which contains relatively a small amount of fiber, shows 

 a water-content of 75 per cent or more. When the plant 

 contains a larger number of thick-walled cells, or woody 

 tissues, which may be required for protection, support, 

 or conduction, the percentage of water may be lessened. 

 In every case, it is probable that the active protoplast 

 requires a water-content of from 80 to 90 per cent or more. 

 The necessary water must be obtained by absorption from 

 the environment, and in the case of the common agri- 

 cultural plants absorption is almost exclusively by means 

 of the root-system. 



The amount of water contained in different plants, or, 

 in fact, in the same plant, is subject to considerable varia- 

 tion. Nevertheless, it is instructive to note the composi- 

 tion of a number of crop or useful plants with respect to 

 this factor. The following table will indicate approxi- 



