72 



BARRINGTON MOORE 



Vol. Ill, No. I 



All species responded, but not equally, to the humus by a very marked 

 increase in rate of growth. The response of Jack pine and pitch pine was 

 considerably greater than that of red pine and cedar (see figs, i and 2). 

 Jack pine and pitch pine are largely confined to the poorest and sandiest soils 

 within their ranges. It may be that their strong response to humus is corre- 

 lated with the character of the soil on which they ordinarily grow, and that 

 they are able to persist on poor sandy soils because of this very ability, for 

 there is always a considerable amount of humus mixed in with the sand of 

 their natural habitat. The response of red pine and cedar to humus would 

 be proportionally less than that of Jack pine and pitch pine, hecause they need 

 other elements in the soil. It would seem that the greater the response to 

 humus, the poorer the soil on which a coniferous species will thrive. Of 

 course, the matter is not so simple as this, and will require much critical work 

 on the availability of the various components of the soil solution, as well as 

 on the physiological processes of absorption and metabolism, before any such 

 law can be stated. 





^25-P)NE- 



:i: 





< 



JACK 



-PI N EH 



^^30- 



PITCH 

 PINE- 



Fig. 3. Growth of coniferous seedling roots in length on unlimed soils, showing 

 the influence of humus. Root area would have shown even greater influence. 



Cedar, curiously enough, grew on the pure sand and on the pure humus. 



The rate of growth fell off earlier in the season — by about July 8 — on 

 sand than on any other soil ; on the mixture of sand and humus it diminished 

 a little later, while on the pure humus a high rate was maintained by most 

 species until the last measurement on September 12. 



