RELATION OF STIMUU TO CONE PRODUCTION 17S 



rate of 0.19 inch diameter and about 1.25 feet in height annually pro- 

 duced a larger amount of germinable seed than trees which grew at a 

 slower rate. This, however, may be indirectly the effect of the age of 

 the tree, since the younger trees have not yet passed the period of most 

 rapid growth." In conclusion number three he points out that young 

 trees from 72 to 100 years old bear more germinable seed than old 

 trees, and in conclusion two that "the largest amount of germinable 

 seed was invariably produced by trees" of the dominant and codomi- 

 nant classes. 



G. A. Pearson, in his work on the seed production of western yellow 

 pine (loc. cit.), states that "a comparison of yellow pine and black jack^ 

 shows an average yield of 1.8 bushels of cones per tree for the former 

 and one bushel for the latter." He attributes this difference mainly to 

 a difference in size of the tree. He also says : "The yield of trees 

 suffering from suppression and attacks of bark beetles and mistletoe 

 are all much below the normal trees of their class." And further: 

 "The yield decreases as the density of the stand increases." 



Location of Cones. — It was found that a single limb on a tree may 

 bear an exceedingly heavy crop of cones, although the remainder of 

 the tree be practically barren of cones. In such cases it could not be 

 found that there was any special relation between the location of the 

 limb on the tree and the direction of greatest light or warmth. 



This irregularity of seed production indicates and suggests that the 

 heavy production of cones by individual hemlocks is due in great meas- 

 ure to causes or stimuli, of which the following are the most obvious, 

 if not the most important. Hemlocks, of course, bear cones without 

 the aid of these stimuli : 



Fire. — A tree which is so scorched that is is wounded quite severely 

 almost invariably responds with a heavy cone crop. Hemlock has such 

 a thin bark and its roots are so close to the surface of the ground that 

 a light ground fire is sufficient to stimulate the tree. 



Insects. — The action of bark-boring insects is a decided stimulus to 

 cone production. (The action of defoliation insects was not observed.) 

 If the infestation be not so serious as to fatally wound the tree and yet 

 be continuous, the tree will be likely to bear heavy crops for several 

 years in succession. 



This is especially the case if the tree is growing rapidly on a good 

 site. 



'Black-jack trees are western yiUow pine trees of a younger generation than 

 are the more mature (western) yellow pines. 



