132 Plant Physiology 



water less valuable physiologically. Any tendency in 

 this direction results in a similar inclination to xerophyt- 

 ism in the flora which may occupy these waters. From 

 the standpoint of the relations of vegetation in general, 

 the water of the sea is to be regarded as almost unavailable 

 physiologically, on account of the large content of salt 

 which it contains. Flowering plants which grow in salt 

 marshes are often, therefore, typical xerophytes. 



71. Semi-xerophytism and hard-wheat production. - 

 The hard-wheats are species or varieties which, for the 

 perfection of their particular economic qualities, require a 

 relatively small water-supply. They are the varieties now 

 cultivated in much of the Central West immediately west 

 of the hundredth meridian. In this section the precipi- 

 tation during the growing season is so inadequate as dis- 

 tinctly to shorten the growing period. This is, moreover, 

 emphasized by the high temperature of the summer season. 

 Other factors may play a part, but in general the growing 

 season is determined by the conditions mentioned. 



This shortening of the growing season is apparently 

 wholly comparable to incomplete maturity. The hard- 

 wheats have a tendency to produce high nitrogen content, 

 and immaturity accentuates the relative increase in pro- 

 tein material and sometimes seems even to augment the 

 total absorption of nitrogen. At any rate, in high nitrogen 

 content, or gluten, lies the advantage of these wheats for 

 semolina and other purposes (including bread-making) 

 to which they are put, so that there exists an interesting 

 relation of region to product. 



The hard-wheats have, for the most part, originated 

 under conditions more or less similar to those prevailing 



