244 JOHN ERNST WEAVER 



The soils on the sheltered slopes were much more open in 

 texture at all depths, and roots were removed with much greater 

 facility than on south slopes where it was often necessary to use 

 a pickaxe to open the trench. 



Root-systems were examined on the southwest slope, and on 

 a northeast slope, both, respectively, near the stations where 

 factor determinations were made; and also on a northwest slope 

 near the station where deep soil moisture samples were taken as 

 a check (see table 3). It should be made plain here that this 

 last station was on a slope only slightly north of west but sheltered 

 by a low westward extension of a ridge in such a manner as to 

 combine more nearly northside substratum conditions with the 

 aerial conditions, as regards exposure to wind and sun, approach- 

 ing those of a south slope. 



A biotic factor affecting soil texture and one which shows a 

 marked effect upon root-systems is the earthworm, a species of 

 Lumbricus. The soils of north and northeast slopes especially, 

 were literally honeycombed with holes ranging from 7 to 8 mm. 

 in diameter and reaching depths of over 13 feet. (See fig. 6.) 

 In the soil of south slopes the work of earthworms is much less 

 in evidence, — perhaps less than half as many holes occur he:ce. 

 Black soil was noted in these burrows at depths of 9-13 feet, 

 perhaps in part worm-casts and in part surface soil washed 

 down from above. Certainly these holes play a large part in 

 the penetration of soil water, and it seems that the additional 

 aeration they afford in these fine-textured soils might be of great 

 importance. 



All the roots examined were of mature perennial plants. The 

 practice followed was to examine six or more roots of a given 

 species and then to write a working description of the roots. 

 These descriptions were kept at hand in the field and as new 

 roots of the same species were studied any variation from the 

 original description was carefully noted. It is believed in this 

 way that thoroughly reliable results have been obtained for 

 the species studied. 



A few of the root-systems were photographed in place, but 

 most of them were removed from the soil and afterward photo- 



