90 Development and Activities of Roots of Crop Plants. 



The differences found in the lesser height-growth, smaller yield, and less 

 extensive underground parts, going from the more mesophytic eastern stations 

 to those of greater aridity westward, correlate directly in nearly every way 

 with the growth of native vegetation, whether trees, weeds, or species of the 

 native grass land are considered. The native vegetation growing through 

 a long period of years integrates the climatic conditions during its growth. 

 Thus it is not only an expression of the present conditions, as is true largely of 

 rapidly maturing crops, but is to a large extent a record of conditions that have 

 obtained during a period of many years. 



The favorable climate for tree-growth at Peru is indicated not only by the 

 large number of species present, but also by their development both in diam- 

 eter and height. At Lincoln, forests are confined to the flood-plains. The 

 species are much fewer in number and the trees are smaller both in diameter 

 and height (c/. Pool, Weaver, and Jean, 1918). Only a very few species occur 

 along the streams at PhilUpsburg, and these are noticeably smaller in every 

 way than those at Lincoln, while the few drought-enduring species which 

 can grow only under cultivation on the plains at Burhngton are even smaller 

 of stature. 



The variety and abundance of the weed flora of eastern Nebraska, as well 

 as the rank growth of the plants, stand in striking contrast to the paucity of 

 species, their lesser abundance, and poorer development at the western 

 stations. Very marked differences occur even between Philhpsburg and 

 Burhngton, low water-content of soil, except in early spring, almost constantly 

 inhibiting normal growth at the latter station. Such widely distributed 

 species as Grindelia squarrosa and Amaranthus retrojlexus reach heights of 3 

 or more feet in eastern Nebraska, but are often hmited to a growth of 6 to 12 

 inches in western Kansas and eastern Colorado. The dwarfing of Festuca 

 octofiora and Lappula occidentalis often to 2 inches or less in the buffalo-grama 

 sod at Burhngton is in marked contrast to their better development under 

 more favorable growth conditions. 



The height-growth of the native plant-cover becomes less, in general, from 

 Peru and Lincoln westward. This is due in a large measure to the lesser 

 abundance or complete disappearance of many of the tall-grass dominants 

 in the mixed-prairie association and a greater abundance of buffalo-grass, 

 grama-grass, and certain carices, but also to the poorer development of 

 many species in the drier habitats. Such diminution in height-growth has been 

 noted repeatedly, while actual measurements of a large number of species, 

 including Agropyrum glaucum, which ranges throughout the area, shows the 

 vahdity of this statement. A study of the growth of seedUngs and transplants 

 at the several stations (Clements and Weaver, 1921) affords conclusive proof. 

 Similar results were obtained during 1919, when rye, oats, and wheat were 

 measured at 14 different stations. Using the height-growth in the true 

 prairie as unity, the ratios for mixed-prairie and short-grass plains were as 

 follows: rye 100 : 66 : 56, oats 100 : 94 : 85, and winter wheat 100 : 85 : 64. 

 Less favorable growth conditions westward are further indicated both by the 

 smaller number and poorer development of societies of subdominants in the 

 grassland (c/. Clements, 1920). 



The actual plant production of the native vegetation also correlates directly 

 with that of cultivated crops. During 1920, 30 square-meter quadrats were 

 cut in the undisturbed grassland at each of the several stations. When 



