CLIMATE AND PLANT GROWTH. 71 



least, by the difference between the water requirements of the aerial 

 parts of the plants, including the fruit or seeds (such as the heads 

 of wheat) , and of the aerial portion without the seeds, the specimens 

 with the best developed seeds, of course, having the highest water 

 requirements. 



4. The water requirement for the production of a unit weight of 

 dry matter is greatest in the oak-brush type, lowest in the aspen-fir 

 type, and intermediate in the spruce-fir type. These relations coin- 

 cide with the relative intensities of the evaporation. 



5. In the case of all species employed, the total, and, indeed, the 

 average leaf length and total dry weight produced are notably great- 

 est in the aspen-fir association, these activities being rather similar 

 in the spruce-fir and oak-brush types. The decreased production in 

 leaf length and the production of dry matter in the respective types 

 are in direct proportion to the evaporation. 



6. The elongation of the stem is greatest in the oak-brush type, in- 

 termediate in the central type, and least in the aspen-fir type. Thus 

 stem elongation appears to be determined largely by temperature and 

 seems to be little influenced by the intensity of the evaporation. 



7. The efficiency of the leaves per unit area as manufacturing 

 agents — that is, in the production of dry matter, appears to vary 

 inversely with the evaporation, though, indeed, temperature appears 

 to be one of the important factors. The largest amount of dry mat- 

 ter per unit of leaf area is produced in the aspen-fir type and the 

 least in the oak-brush type, while in the spruce-fir type, where the 

 evaporation is only slightly less intensive than in the oak-brush 

 type, the dry matter produced is only slightly greater than in the 

 oak-brush type. 



CONCLUSIONS. 



From the study here reported, it may be concluded that in this 

 locality Kubanka wheat and Canadian field peas, and doubtless 

 other agricultural crops, can not be grown profitably at elevations 

 exceeding about 8,000 feet because of the lack of sufficient heat. As 

 has been shown by the crop production of the region, enough heat 

 units were produced in the seasons studied up to an altitude of about 

 8,000 feet, which includes most of the oak-brush type, to mature 

 wheat, peas, and certain other crops. The amount of precipitation 

 received at an elevation of 8,000 feet and lower, however, was below 

 the requirements of crop production, indicating that the lands must 

 either be irrigated or the moisture conserved by thorough summer 

 fallowing. The native forage crop produced in the oak-brush type, 

 on the other hand, is fairly luxuriant, and if properly utilized will 



