PLANT GROWTH IN DRY AREAS 105 



for existence the more are the energies of the plants 

 centered in producing the elements that relate to repro- 

 duction. 



The growth of plants in dry areas is nearly all made 

 early in the season. This is more especially true of 

 areas in which the precipitation, or much of it, falls dur- 

 ing the period of early growth. The grasses of the prai- 

 rie as a rule cease to make appreciable growth after July, 

 whereas the grasses in humid areas usually make much 

 growth in the autumn, and in many instances continue 

 to grow on until the closing in of winter. The partial 

 and oftentimes complete cessation of growth after mid- 

 summer is the outcome of the lack of moisture in the 

 soil, and this is further accentuated by the lack of mois- 

 ture in the air. This it is that makes it so important that 

 land on which winter crops are to be sown shall have 

 the moisture conserved by proper cultivation during the 

 summer previously. In some limited areas, as in the 

 upper Flathead valley for instance, enough moisture 

 falls in the autumn to result in a more or less free 

 autumn growth. 



That production in dry areas will be less certain 

 than in humid areas, at least in some of its phases, can- 

 not be gainsaid. This results from variation in the an- 

 nual precipitation and in the time of the same. It does 

 not follow that the actual variations in the precipitation 

 will be greater in dry than in humid areas, but they will 

 be felt more. In dry areas the precipitation is seldom 

 or never beyond the best needs of the crops in a normal 

 season, while in humid areas an excess of moisture is 

 not infrequent. The crop in dry areas will take harm 

 usually in proportion as the shortage from the normal 

 increases, whereas an equal decrease in the rainfall in 

 humid areas may do but little harm. From what has 

 been said the necessity for the proper conservation of 



