CLIMATE AND PLANT GROWTH. 



45 



full maturity. 1 In the case of Experimental Series No. 1, in which 

 the standard plants were started simultaneously in all types as soon 

 as the temperature favored growth in the highest type, wheat heads 

 filled well in the aspen-fir type but killing frosts occurred before the 

 caryopsis hardened thoroughly; in the type above, growth was ar- 

 rested when the heads were still in a developmental stage. Kecords 

 of these plant specimens, supplemented by those of the late planted 

 batteries (Experimental Series No. 2) afforded data as to the relative 

 water requirements of plants in different stages of development. 

 Because of the difference in age of the plants in the early planted 

 and later planted batteries, the two sets of specimens were really sub- 

 jected to different environmental conditions, for it is well known 

 that the same weather factors do not affect plants in different stages 

 of development in the same way. For this reason the water require- 

 ments of the two sets of plants may not be entirely comparable. 



For the purpose of comparisons between the water requirements 

 of the entire tops of wheat and brome-grass specimens, heads in- 

 cluded, and tops without the heads, the dry matter of the specimens 

 with and without heads was recorded and the water requirements of 

 each determined. The results are summarized in Table 13. 



TABLE 13. Relation of water requirements of wheat and brome grass, to effective 

 temperatures in climatic types. 



WHEAT (EXPERIMENTAL SERIES No. 1). 



WHEAT (EXPERIMENTAL SERIES NO. 2). 



BROME GRASS (EXPERIMENTAL SERIES No. 1). 



The above values, platted in figures 24, 25, and 26, exhibit a 

 gradual falling off from the lowest to the highest station in the ratio 



1 Owing to the early maturing qualities of mountain brome grass, this species more 

 nearly reached maturity in all types than did the cultivated plants. 



