184 Forestry Quarterly. 



firs, highly dependent on moisture, found enough light and cor- 

 responding to it sufficient soil moisture. 



The third year (1908) the spruces still hung on, while the 

 firs and oaks were thriving. Douglas Fir and Oak grew better 

 in the isolated, Nordmann Fir showed no difference, spruce did 

 worse in the isolated plat. 



Practically, the influence of varying soil moisture on incre- 

 ment can exist only within the limits of light supply required by 

 the biological character of the species. 



A further check test was made in the Douglas Fir stand, re- 

 planting the old plats and treating them the same as before, but 

 adding a fourth one in an opening with only top light, which ad- 

 mitted one-eighth of the full daylight. At the end of the year the 

 plants on the last plat showed better than on the other plats. In 

 July of the second year, the difference was still greater, the toler- 

 ant firs could not persist in the shadier plats, even though watered, 

 while in the opening a number of pines even had persisted. 



Finally a last test was made in the Douglas Fir stand by placing 

 4 boxes 16 inches deep, the bottom consisting of narrow-gaged 

 wire netting, filled with the same kind of prepared soil and planted 

 with a number each of nine species ; after the boxes had been 

 kept well watered in open light, two of these were placed, sunk 

 into the soil in an opening, the two others, 25 feet from the first, 

 in dense shade. One box in each set was kept well watered when- 

 ever it had not rained for three days. By the end of June all 

 larches had succumbed in both boxes in the shade, the pines being 

 sickly; by the end of September all the plants in these boxes 

 watered or not, were dead or dying. Those in the other set, out- 

 side of Scotch, White Pine and Larch which had mostly suc- 

 cumbed, were in good condition, no difference between watered 

 and unwatered box being visible. The next year merely ac- 

 centuated the relation. In the opening all larch, all pines, except 

 one White Pine had died, firs, beech, and oak remaining in good 

 condition, less so spruce and Douglas Fir, the watering making 

 no difference. 



This last step, then, also demonstrated that an optimum of soil 

 moisture can be of use to an undergrowth under the crown cover 

 of an old stand only when there is a light intensity, which ex- 

 ceeds the minimum of light requirement of the species. Hence, 



