FACTORS INFLUEXCINC, REPRODUCTION 839 



bearberry {Arctostaphylos uvi-ursi) , and other members of the heath 

 family, grasses, a Httle golden rod, and a few other plants. This is 

 followed closely by ground juniper (Jttniperus communis) , pitch pine 

 coming in with the juniper or shortly afterward. Under the pitch pine 

 there are dense groups of huckleberry (Gaylussacia haccata). Repro- 

 duction of pitch pine is fairly abundant in the openings, but seedlings 

 of white pine predominate. Mixed with the white pine are scattered 

 seedlings of fir and a few of spruce, indicating that the stage succeeding 

 the pitch pine will be composed chiefly of white pine with a little fir 

 and an occasional spruce. Red pine often comes in with the pitch pine 

 on the more favorable spots and remains in the white-pine stage. 

 Lastly, spruce seeds in under the white pine and fir, and eventually 

 predominates except on the dry south aspects. The final stage may, 

 however, except on the moister sites, retain a considerable proportion 

 of white pine. On moist fiats cedar comes in soon after the pitch pine 

 and takes possession. 



EXPERIMENTS 



The main experiment was designed to find the effect of soil acidity 

 on the growth of sprvice and fir seedlings. The predominance of fir 

 reproduction under stands of spruce has always puzzled foresters and 

 has been tentatively explained in a number of ways, but has never been 

 studied experimentally. The most commonly accepted explanation is 

 that the spruce renders the soil acid and unfavorable to its own repro- 

 duction, and that fir is more tolerant of acid, and hence is at an advan- 

 tage in reproducing under spruce stands. If this h}'pothesis is correct, 

 spruce should be more adversely affected by acid soils than fir. It 

 might even be that fir not only tolerated, but required, acid, like blue- 

 berry, which Coville'^ found could be grown only on acid soils. 



In order to determine the comparative effect of acidity on spruce and 

 fir, seedlings of these species were transplanted from the forest into 

 three different kinds of soil. White-pine seedlings were also trans- 

 planted, but only two were placed in the raw humus. The seedlings 

 were of approximately the same size and were taken from the same 

 place, so that variations due to size and vigor were eliminated.^ 



' See citation given under note 4. 



'Nachtigall (Forstwissenschaftliches Centralblatt, pp. 55-75 and 131-150, 1916; 

 Review in Forestry Quarterly, Vol. 14, pp. 514-517, 1916) shows that the rate of 

 growth varies, other things being equal, with size and age. Accordingly tests 

 were made to determine if this would affect the results in this case, and it was 

 found that the small variation in the size and age of the plants used in this 

 experiment was without influence. 



