THE SANDHILLS SUBCLIMAX. 



79 



In the first foot of soil scarcely any laterals originated, but below this point 

 both large and small branches came off in great abundance. These varied in 

 diameter from less than 1 mm. to half an inch. While a very few ran some- 

 what vertically or obliquely downward, the general course of most of them 

 was quite parallel with the soil surface. The lateral spread was enormous, 

 the roots running off to distances of 15 to 25 feet or more. One of the larger 

 forks of a root, 0.5 inch in diameter, was traced to a distance of 14 feet and at 

 a depth varying from 25 to 30 inches from the base of the plant, when it 

 branched into two equal parts, 4 mm. in diameter. These wide-spreading 

 laterals sent off abundant branches, many of which passed off at right angles, 

 either vertically downward or vertically upward, for distances of many feet. 

 Indeed, the surface foot of soil as well as the 10 feet below it were literally 

 filled with the glistening white, brittle branches of this remarkable root system. 

 The ultimate branches, however, while occurring in great numbers, were not 

 profusely divided. The great network of roots originating at a depth of 5 feet 

 is well shown in figure 30, but because of the caving of the sandy soil it was 

 impossible to follow them to a greater depth. However, judging from their 

 diameters of 2 to 4 mm. at this level and the nature of the other roots examined, 

 it is highly probable that they penetrated many feet deeper. The enlarged 

 portion of the tap-root not only furnishes an enormous reservoir for food, but 

 also a storehouse of water upon which the plant may draw during a period of 

 drought. 



SANDHILL ROOT SYSTEMS AND THE SANDHILL ENVIRONMENT. 



Eight of the 19 sandhill species examined^ have roots which are 

 entirely or nearly confined to the first 2 feet of soil. Of the others, all 

 but one have their main root development in the first 2 or 3 feet of 

 soil. Even the very deep-rooted Eriogonum microthecum and Arte- 

 misia filifolia show a striking profusion of long, wide-spreading laterals 

 in this soil layer. Indeed, it will be shown later that Stipa comata, 

 Bouteloua gracilis, and Chrysopsis villosa, all rather deep-rooted plains 

 species, become rather shallow-rooted under sandhill conditions. 

 Among the grasses the rhizome habit is extremely well-developed, 

 while long, rather horizontal, shallow laterals are characteristic of 

 most of the plants examined. In this soft substratum such a root 

 habit can not be attributed to the mechanical difficulty of penetration, 

 but seems closely related to the water-supply. 



Rainfall is at once absorbed and there is practically no run-off, even 

 in the heaviest showers. As soon as the storm passes, evaporation 

 dries out the surface sand with great rapidity, but to a slight depth 

 only. This surface layer of dry sand forms an excellent mulch, which 

 has a wonderfully retarding effect upon further evaporation. At a 

 depth of but a few inches below the surface the sand is always moist 

 and may usually be molded into lumps by pressure of the hand. The 

 vegetative cover is usually rather sparse and consequently water- 

 losses by transpiration should be much less than on the plains. Unfor- 

 tunately few data on soil-moisture in sandhill soils are available. 



* Only 14 are here described; the others will be found under the section on ecads (p. 110). 



