188 Sub-Artic Soul [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, wnd 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 Howarp E. Puiirne 
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* was a gray to buff colored lacustrine clay 
*The valleys of the Nelson river and its tributaries near Split 
Lake, which is situated in northern Manitoba, Canada, at about 56° 
north latitude and 96° west longitude. 
