July 14, 1911] 



SCIENCE 



57 



a short season for growth, and of a relatively 

 high nutrient content. In connection with 

 the heavier rainfall in June and July, the 

 nutrient content of shortgrass land too often 

 produces a deceptively luxuriant growth of 

 crops, which are cut short by dwindling water 

 content in late July and August. 



The wiregrass association is dominated by 

 Aristida longiseta. It is found chiefly on 

 sandy loam, or at least on soils intermediate 

 between the sandhills and the hard lands. 

 The soil texture in wiregrass land permits 

 greater penetration of rain, available water 

 occurs deeper in the soil, and deep-rooted 

 species become possible. The roots of wire- 

 grass are from 2-3 feet long, while its usual 

 associate, Psoralea, reaches a depth of 5 feet. 

 There is nothing, however, to exclude the 

 short-rooted grasses, and two species of grama 

 often occur in this association. The wiregrass 

 association indicates more favorable condi- 

 tions for crop production than any other 

 group. The soil is sufficiently compact to 

 prevent blowing, and is well-supplied with 

 nutrients. Water penetrates readily to a fair 

 depth, and water loss is lessened by the air 

 content of the sandy surface. 



The soil of bunch-grass land is sand, and it 

 allows rain to penetrate to a greater depth 

 than either the hard land or the sandy loam. 

 It contains more available water than these 

 soils, but is relatively poorer in nutrients. 

 Owing to its loose structure, it blows readily, 

 and methods of cultivation must take ac- 

 count of this fact. The runoff from the sand- 

 hills is negligible, and the water loss from the 

 soil surface slow, owing to the formation of 

 a mulch of dry sand. The typical species of 

 the association, bunch-grass (Andropogon 

 scoparius), develops roots to a depth of 4-6 

 feet, as is the case also with its most frequent 

 associates. The density of bunch-grass seems 

 to be in direct relation to the water supply, 

 and consequently a fairly close cover indi- 

 cates a higher water content and better agri- 

 cultural conditions. When the bunches are 

 scattered, the short-grass finds an opportunity 

 to establish itself in the spaces, utilizing the 

 water content of the first soil foot. 



The final vegetation type of the region is 

 the shortgrass association, which may be 

 reached through various successions. Of the 

 two common primary successions, one begins 

 with lichens on disintegrated rocks, passes 

 into the Outierrezia-Artemisia association, 

 and as the soil becomes finer, terminates in 

 the shortgrass association. The pioneers in a 

 blowout initiate a longer succession. As a 

 consequence of rendering the sand more 

 stable, they yield sooner or later to a mixed 

 association of sandhill plants, and finally to 

 the bunehgrass association proper. The effect 

 of fires or grazing is to change the latter to 

 the shortgrass association, often through an 

 intermediate wire-grass stage. When an as- 

 sociation is destroyed by breaking the soil, 

 the first vegetation wiU consist of weeds, but 

 this will soon be replaced by the association 

 which ordinarily precedes the one destroyed. 

 For example, when short-grass is broken, 

 Gutierrezia-Artemisia or wire-grass will take 

 possession, to yield again to short-grass in the 

 course of two or three decades, bunch-grass or 

 other sandhill vegetation will temporarily re- 

 place wire-grass, etc. The cause of this is 

 readily found in the loosening of the soil, 

 while the reaction which brings back the orig- 

 inal stage is seen in the increasing stabiliza- 

 tion of the soil. 



From the standpoint of crop production, 

 the largest yields are obtained during favor- 

 able seasons from the shortgrass land, but fail- 

 ures are also most frequent on it. Bunch-grass 

 land produces the smallest yield in good 

 years, but on the other hand crop failures are 

 rare. Because of its intermediate position, 

 wiregrass land is usually the most valuable 

 of all, since its productivity is not far below 

 that of shortgrass land in good years, and it 

 has much of the advantage of bunehgrass 

 land in dry years. 



Frederic E. Clements 



The University op Minnesota 



Blumen und Insehien, ihre Anpassungen 

 aneinander und ihre gegenseitige Alhangig- 

 keit. Von Professor Dr. O. von Kirchner. 



