January, 1922 



GROWTH OF TREE SEEDLINGS AND WHEAT 



71 



these curves. With wheat the influence of the humus added to the sand was 

 greater than with the trees, and was more nearly in proportion to the volume 

 of humus in the soil. 



The favorable effect of the humus, either pure or in mixture, was not at 

 once apparent. Germination was more rapid on the sand. If this was due 

 to heat, it must have been on account of the smaller amount of water in the 

 sand even at its optimum moisture content, and possibly to its greater con- 



iB jui^a 



28 Mq.1 



Fig. 2. On left, growth in height of white cedar (arborvitae) seedlings on un- 

 limed soils ; and of red pine seedlings on unlimed and on lightly limed soils ; showing 

 smaller response to humus on the part of cedar and red pine (compare with fig. l). 



On right, white cedar seedlings on lightly limed and on heavily limed soils. 

 Shows later germination on heavily limed humus, and on sand with humus, but 

 relatively less injury from lime than in the case of other species (compare figs, i 

 and 6). 



Sugar maple one-year-old transplants on unlimed soils, showing the influence of 

 humus on the rate of growth in height above the primary leaves. 



ductivity, for the sand was light colored and absorbed considerably less heat 

 than the darker humus. It may be that the seeds absorbed water more rapidly 

 from sand than from humus, because the humus was not thoroughly decom- 

 posed, and hence could not be packed as closely about the seeds as could 

 the sand. 



All species did better at first on the sand than on the mixture of sand and 

 humus, but eventually those on the latter caught up with and passed those on 

 the former; this occurred at about the same time for all trees. It may be 

 that the nitrogen in the humus became available after a certain period of 

 exposure. 



