under the shade of the parent tree, nor of neighboring trees of 

 that species. This fact suggests that conditions in the soil are 

 also a factor. The suggestion is rendered all the more probable 

 by the fact that hemlocks are frequently not among the plants 

 growing in the open areas, and especially by the fact that hemlock 

 seedlings readily develop under the white pine (Pinus strobus), 

 so that the latter species is sometimes replaced by hemlock.* 



The fact that white pine seedlings will not develop under hem- 

 lock may be explained, in part at least, by the fact that the white 

 pine is an intolerant, or light-demanding, species. It fails to de- 

 velop under the shade of oaks, chestnuts, etc., as well as under 

 hemlocks, while hemlock develops easily under the shade of 

 those species. 



It has been asserted f that the seeds of hemlock " cannot ger- 

 minate under the trees that bear them." This certainly is an 



In the hemlock forest in the New York Botanical Garden young 

 seedlings may be observed in the spring in abundance under the 

 trees, even to within less than a foot of the trunk. In no case 

 however, has the writer ever found these seedlings attaining a 

 height of more than eight or ten centimeters (three or four 

 inches). Some cause interferes with their further development. 

 Since the species is a tolerant, or shade-loving one, and since the 

 seedlings may develop into vigorous saplings in the shade of a 

 broad-leaved, deciduous forest, the conclusion seems warranted 

 that their failure to develop near the parent trees is due partly 



It is a well-known fact that many plants, grown in a substra- 

 tum of soil or other nutrient medium, excrete into the substratum 

 substances that are deleterious to that species, so that it is difficult 

 or even impossible, to grow a second or third crop of the same 

 species in the same soil. Thus Livingston % found that wheat 

 seedlings grown in clean glass sand in which wheat had previously 



