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ROOT HABIT AND PLANT DISTRIBUTION IN THE FAR 



NORTH 



HOWARD E. PULLING 

 The Johns Hopkins University/, Baltimore, Md. 



One of the most striking charatfteristics of the landscapes of 

 north-central Canada is the monotony of the sky-line. A jagged 

 horizon of spruce tops meets the eye everywhere except in 

 exceedingly small areas. This predominance of spruce is 

 usually ascribed to a tolerance of low temperatures greater than 

 that characteristic of the dominant trees of more temperate 

 climates. In such a statement the assumption appears to be 

 implied that the direct effect of temperature upon physiological 

 processes 'controls the flora of the far north. It is a purpose of 

 this paper to point out one way in which low temperatures may 

 retard the growth or limit the size of certain species of trees in an 

 indirect way. To form a suitable background for the data to be 

 presented it is necessary to consider briefly some of the char- 

 acteristics of the region. 



Physiographically, northern Canada is extremely young. A 

 bird's-eye view would show the relative proportions of water 

 and land so nearly equal in extent that it would require nice 

 discrimination to determine which is in the excess. The lakes 

 are irregular with rocky shores, lagoons and often abut upon 

 swamps or muskegs. The rivers are alternations of rapids and 

 falls with lake-like expansions of quiet water that are often reed 

 girt and swampy. The land surfaces are characterized by eskers, 

 moraines, drumlins, kames, ispatinows and till among which 

 the scoured and striated rocks of pre-cambrian date are freely 

 and unevenly presented. A large area in the heart of central 

 Canada is occupied by the bed of glacial Lake Agassiz which 

 extended from the northern part of Minnesota to about 57°35' 

 north latitude. This great lake bed embraces the region now 



223 



THE PLANT WORLD, VOL. 21, NO. 9 

 SEPTEMBER, 1918 



