IMPOETANCE OF WATER 253 



constructs the form of a land plant in which it may 

 operate, it must take care that the structure is such 

 that it may draw and hold the moisture which is neces- 

 sary to its being. There be land plants and water 

 plants, but we cannot say there is land protoplasm and 

 water protoplasm, for this vital substance, wherever it 

 may thrive, can do so only in, and by means of, the 

 medium in which it had its birth. 



Water constitutes nearly 50 per cent, of the weight 

 of the woody parts of plants, and in juicy herbs the 

 percentage of water is from 70 to 80. The proportion 

 becomes higher in succulent plants and fruits, varying 

 from 85 to 95 per cent., while in aquatic plants it rises 

 to from 95 to 98 per cent. It is apparent that if we 

 are to know anything about the life of a plant, we must 

 study it in relation to its water-supply. 



We decide that water is of importance to the proto- 

 plasts of a plant as a medium in which they can operate, 

 and which so permeates them that they are maintained 

 in a sufficiently elastic condition and also energized. 

 But water has other important uses, for it conveys 

 valuable mineral salts in solution for the use of the 

 little protoplasmic chemists. It is a transporting agent 

 of the products of their chemistry, and, again, it is an 

 actual food, for the elements of which it is composed — 

 hydrogen and oxygen — are utilized in the preparation 

 of nutrient organic compounds. Cells sufficiently sup- 

 plied with water are turgid, and render a plant rigid. 

 The effect of the turgidity of cells is well illustrated in 

 the commonly cultivated Hydrangea. This plant in 

 warm weather transpires freely, and uses much water. 

 So long as the supply is sufficient, its leaves are rigid. 



