ROOT HABIT !N THE FAR NORTH 229 



Hudson Buy by white spruce, which farther south does not grow 

 in such situations. 



Jack Pine (Pinus Banksiana Lam. ; P. divaricata Gordon) is a 

 decided contrast to black spruce. It is found on drier §oils, 

 deeper soils and often appears after a fire on soil that later sup- 

 ports white spruce. The individual represented in figure 1, 

 of which practically all the roots are shown, was found on the 

 high hill overlooking the portage of the Grand Rapids of the 

 Nelson river (about 56°10'N. lat. and 96°30'W. long.) Judging 

 from experience, the frost line was not less than 2 meters below 

 the surface and since in this case there was no sphagnum carpet, 

 it was perhaps even lower. One long branch paralleled the tap 

 root but became horizontal a few centimeters below the surface 

 of a layer of very dense, compact clay. The tap root, however, 

 showed no indication of becoming horizontal and, judging from 

 other trees investigated, the tap root of this species rarely, if at 

 all, becomes extensively horizontal. Jack pine (2), also figured 

 practically complete, was found on the Brule river in deep sand 

 and shows no noteworthy difference from (1) with the exception 

 that no laterals grew^ parallel to the main root. Since no other 

 tree taken in the north showed this feature it is possible that it 

 has no significance from the present point of view. 



Jack pines have been found, however, growing on rock with 

 very scanty soil. Trees in such situations occur on the east shore 

 of Nipigon lake in northern Ontario. But in every case examined 

 it was found that the roots penetrated fissures in the rock and 

 did not form a root-mat over the surface n the same way the 

 spruces did. In consequence, the occurrence of jack pine in 

 these situations was only occasional. The long, horizontal, 

 surface roots, coupled with the deep tap root may indicate that 

 the plant is able to utilize both surface and deeper water supplies. 



Jack pine is apparently found as far north as deep soil is found, 

 the limiting ice barrier in the ground being often lowered when 

 moss fires have bared the surface to the sun's rays. It is possible 

 that the shading produced by the growing trees themselves may 

 increasingly hinder this summer thawing so that groves of jack 

 pine may later be killed almost simultaneously from this cause. 



