January, 1922 



GROWTH OF TREE SEEDLINGS AND WHEAT 



73 



but not on the mixture of sand and humus. The reason is unknown, unless 

 it be that cedar will not tolerate acidity unless the acidity be compensated for 

 by an abundance of humus. Fernald has shown (2) that cedar exhibits a 

 marked preference for calcareous soils; the writer has found much cedar 

 growing on Mt. Desert Island, Maine, where the soil was not calcareous, but 

 contained abundant humus. 



Grozvth of Roots and Green Weight.— The influence of the humus on 

 root growth was as marked as its influence on height growth. The roots 

 were not only longer, but more branched, and therefore had a much larger 

 absorbing area than on the sand. In spite of the shallowness of the flats the 

 roots on the humus attained lengths of from 20 to 30 cm., as against 10 to 

 13 cm. on the sand, and 11 to 20 cm. on the mixture of sand and humus 

 (Table i). 



The effect on the growth of roots in length is shown in Table i and repre- 

 sented graphically in figure 3. This gives only part of the influence of humus, 

 because it ignores the branches, and hence does not represent differences in 

 total root area. Had it been practicable to measure the length of all the 

 branches, the influence of humus would have been exhibited even more 

 strikingly. 



Table i. Growth of roots in length, unlimed soils 



Species 



Soil 



Average length, cm. 



Sand 



Sand with 4% 

 humus by weight 



Humus 



Jack pine. 

 Pitch pine 

 Red pine . 



20 

 II 



30 

 30 

 20 



The roots of Jack pine and pitch pine were longer than those of red pine, 

 as would be expected from the drier and poorer soil in the native natural 

 habitat of these species. It is not, however, safe to draw general conclusions 

 as to the relation of depth of root to moisture and- fertility requirements, 

 because the response may be due to one of several factors, among which are 

 not only moisture and fertility, but soil oxygen. 



The influence of humus on green weight per seedling at the end of the 

 growing season is given in Table 2 and shown graphically in figure 4. Al- 

 though the difference between the pure sand and pure humus is very marked, 

 the difference between the pure sand and the sand with 4 percent humus by 

 weight, though distinct, is not very noticeable. The greater response which 

 Jack pine and pitch pine make to humus, as compared with red pine, shows 

 in the green weight as in the height growth. 



