188 Sub-Artie Soil [386 



an area of 30 square millimeters. If the water contents per 

 unit of gross volume of a number of such samples of the 

 same soil are plotted as ordinates, and the corresponding dry 

 weights are plotted as abscissas, the graph obtained by con- 

 necting the points is the positive portion of an approximately 

 paraboliform curve that is symmetrical about the horizontal 

 axis. This graph ascends steeply in the region of light pack- 

 ings, indicating the relatively large effect of adding more 

 soil to a volume of low soil content. Its tendency to become 

 horizontal indicates that, with dense packings, the addition 

 of more soil but slightly increases the water content at the 

 dynamic minimum. 



The amount of water that exists in a given soil at a given 

 packing above the minimum point for that packing is sub- 

 ject to capillary movement, so that the determination of the 

 minimum is of great value in calculating the maximum rate 

 at which water may move through the given soil under those 

 conditions. Because the graphs vary in height and slope, 

 at corresponding points, from one soil to another they should 

 also serve as soil characteristics by which various soils might 

 be recognized. 



SOME UNUSUAL FEATURES OF A SUB-ARCTIC SOIL 



By HOWARD E. PULLING 



A preliminary survey of the ecological features of some 

 sub-arctic forests during the past summer yielded informa- 

 tion concerning the soils that emphasizes the need of in- 

 cluding the physical root -environment in an ecological study 

 of such regions. The chief soil over the major portion of 

 the area visited 1 was a gray to buff colored lacustrine clay 



1 The valleys of the Nelson river and its tributaries near Split 

 Lake, which is situated in northern Manitoba, Canada, at about 56 o 

 north latitude and 96 west longitude. 



