ECOLOGY. 



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The same relation was determined not only for oats, wheat, and barley, but 

 also for aKalfa and sweet clover as well as for maize. For example, the dry 

 weight of stalk of maize was, in the above sequence of stations, 64, 83, and 100 

 per cent and the dry weight of ear was 45, 59, and 100 per cent. Thus, 

 native and crop plants are shown to integrate environmental conditions and 

 to express them quantitatively in yield. 



Relation of Holard to Root Development and Yield, by F. C. Jean and 



J. E. Weaver. 



Crops of Marquis spring wheat, corn, alfalfa, sugar-beets, and potatoes 

 have again been grown in plats of one-thirtieth of an acre each at Greeley, 

 Colorado, on dry land and under semi-irrigated and fully irrigated conditions. 

 The main objective was to determine the effect of different quantities of 

 water on root development and yield. The root development of each of the 

 crops was studied in several stages of growth under each environment. The 

 rainfall during the past summer has been abnormally high, and the factors 

 of temperature, humidity, and evaporation, (continuous records having been 

 kept during two seasons) as well as the holard, are very different from 1922. 

 However, none of the aerial factors at the several stations were very different 

 for either season, so that after allowing for physical and chemical differences 

 of the soil direct correlations with variation in root habit and holard were 

 determined. Root development in the dry land was hmited by the depth 

 of moist soil, the roots of all crops being largely confined to the surface 3 feet. 

 Major branches were most abundant in the surface 18 inches and showed a 

 more marked tendency to penetrate downward than those in the fully irri- 

 gated plats, which also often originated at greater depths and spread widely 

 in the moist mellow soil. Depths of 5 to 8 feet were commonly reached by the 

 root systems under the latter conditions. Smaller branches were greater 

 in number, longer, and more abundantly rebranched in the dry land. In 

 semi-irrigated soil, conditions were intermediate, deep penetration being 

 accompanied with profuse branching. For example, fully mature corn reached 

 working depths of 32, 40, and 58 inches in the dry-land, fully irrigated, and 

 semi-irrigated plats, respectively, the stalks in the dry land being 3 feet and in 

 the irrigated fields 7 feet tall. Maximum depths in the same sequence were 

 44, 70, and 80 inches. The rate of branching ranged from 20 to 25 per inch 

 in dry land (average length 4 inches) to 12 to 20 (average length 2 inches) in 

 fully irrigated soil. The moister soil of 1923 gave an excellent opportunity 

 of studying root behavior in the same soil under different degrees of water- 

 content. 



