290 



JOHN ERNST WEAVER 



here described (with the possible exception of Leptotaenia multi • 

 fida) fall under the generalized class. By a generalized root- 

 system is meant one that has both the tap and the laterals well 

 developed. They penetrate deeply and reach out widely. In 

 contrast, the specialized root-system has either the tap root as 

 the chief feature, or the laterals are placed near the surface, and 

 especially well developed, as in cacti. The generalized type of 

 root is much more plastic and consequently reacts to a wider 

 range of conditions than does the specialized type. 



In considering the question of the susceptibility of roots to 

 modification through variation in the soil texture or its water 

 content, as against the conservative inheritance tendencies, table 

 6 is instructive. 



TABLE 6 

 Average root depths of plants on different slopes 



Lupinus ornatus 



Lithospermum ruderale. . 

 Potentilla blaschkeana. . 

 Geranium viscosissimum 

 Hoorebekia racemosa. . . . 



Hieracium scouleri 



Helianthella douglasii. . 

 Balsamorhiza sagittata. . 

 Leptotaenia multi fida. . . , 

 Agropyron spicatum 



S. W. SLOPE 



i7iches 



72.1 



64.0 

 62. S 

 52.0 

 61.5 



N. E. SLOPE 



inches 



71.0 

 48.7 

 59.2 

 56.1 

 63.4 

 63.4 

 55.6 



54.7 

 49.6 



N. W. SLOPE 



inches 



128.4 

 74.5 

 64.3 

 72 

 68 

 66 

 55 

 69.8 

 47.3 

 38.6 



It appears that the root lengths on northeast and southwest 

 slopes are about the same and that the marked environmental 

 differences play little part in determining root depth. However, 

 the writer is of the opinion that the hard soil on dry southwest 

 slopes is a limiting factor to root growth. When we note the 

 greater root development on the northwest slope, which, as has 

 already been pointed out, combines a porous moist soil with 

 rather extreme xerophytic above-ground conditions, this con- 

 clusion would seem to be warranted, although the evidence 

 of Leptotaenia and Agropyron is to the contrary. But more data, 



