PERIODICAL LITERATURE 443 



said to suffer from drought during the summer, as a result of which 

 a number have died. 



Abies concolor is the only one of the firs that has proved to be 

 vigorous. Cedrus dcodara, like the Atlas cedar and the cedar of 

 Lebanon, is slow growing, but maintains its growth better than those 

 species and is also ornamental. Picea excclsa has not done so well as 

 P. mencicsii. 



Among the American conifers special mention is made of Psciido- 

 tsuga douglasii (taxifolia) , which attains a diameter of i8 centimeters 

 and a height of 4 meters. It is regarded by the author as a tree of 

 the future which grows on the most unfavorable soils. 



S. T. D. 



Les Meilleures Essences de Boisement dans Region du Centre. L. Chancerel. 

 Revue des Eaiix et Forets. February, 1919, Vol. 57, pp. 31-33. 



The preponderance of spruce in north-central 



Root Habits Canada is usually ascribed to its greater tolerance 



of Trees in of low temperatures than that of the predomi- 



Northern Canada nating trees of the more temperate climates. It is 

 frequently inferred that the direct effect of tem- 

 perature upon physiological processes controls plant distribution in 

 the far north. Howard E. Pulling shows how low temperatures may 

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

 indirect way. 



The root habits of Picea mariana, Pinus banksiana, Larix laricina, 

 Betula papyrifera, Populns balsamifera and Pinus strobus were stud- 

 ied in the Province of Manitoba between latitude 55° N. and 56° N., 

 and longitude 96° W. and 98° W. in a uniform clay soil and in a 

 sandy soil near the south shore of Lake Superior in Douglas Countv, 

 Wisconsin. The main characteristics of the root systems are exhibited 

 in dimensioned figures. The soil was found to be generally shallow 

 and frozen at depths ranging from 2 meters on the exposed south 

 slopes to 3 cm. on flat benches with a northern exposure which acted 

 as a mechanical barrier to root penetration. 



These trees were found to differ not only in their root habits, as 

 they do in their top habits, but also in the rigidity with which the 

 habits are maintained under varying environmental conditions. This 

 investigation is summarized as follows : 



Root systems may be classified as deep whtn the habit is centered 

 about a main deeply penetrating tap root and shallow when such a tap 

 root is absent, and the roots remain near the surface of the soil. 



