846 JOURNAL OF FORESTRY 



The fir roots responded to soil differences in the same way as spruce, 

 except for branching. In fir there was somewhat more branching on 

 the mild humus than on the raw humus. In fact, one of the chief 

 characteristics of fir on the raw humus was the length of new root 

 growth without branching. This agrees with the natural habit of the 

 tree. Fir roots in the forest are always much less branched than those 

 of spruce, a character of importance in competition when the two trees 

 grow on the same site, and also accounting to a certain extent for the 

 frequent occurrence of each on different habitats. For example, the 

 branching superficial habit of spruce confines the tree to sites with 

 abundant surface moisture and lays it open to danger from windfall. 

 Fir, on the other hand, appears to be able to grow on somewhat drier 

 sites and on the mountain tops exposed to severe winds. There are, 

 of course, other characteristics which play an equal, if not greater, part 

 than the roots in these habitat differences. 



The fir roots on the mineral soil were not only less thrifty than on 

 the mild humus and raw humus, but were in some cases badly infested 

 with a black fungus which is common on spruce, fir, and white pine in 

 the forest. There was but little of this fungus on the other two soils. 

 This, with the fact that in the forest the fungus attacks some roots and 

 not others on the sartie plant, would indicate that the occurrence of the 

 fungus is correlated with low root vigor rather than with abundance of 

 fungus spores ; for the spores must have been even more abundant in 

 the raw humus than in the mineral soil. 



In order to secure a rough numerical idea of the dift'erences between 

 the root development of the same species on the different soils, measure- 

 ments were made of the season's root growth on the main root and on 

 from one to three branch roots of a few plants taken at random from 

 each flat. The averages of these measurements are given in Table i. 



Table I. — Influence of soil on tlie length of root growth in spruce and fir 



Acidity Length of average root growth for the 



, -^ ^ season in millimeters 



Coville Truog ,. ^ ^ 



method method Spruce Fir White pine 



Mild humus neutral neutral 76 106 90 



Raw humus a 002 strong 60 88 note 



Mineral soil 00017 medium 30 39 74 



o Raw humus had onlj' two white-pine transplants, averaging 131 millimeters. 



Since the root measurements were made at the end of October, while 

 the measurements of the tops were concluded when the growth in length 

 ceased (July 10 for fir and August 10 for spruce and white pine), it is 

 not to be expected that there should be complete agreement between the 



