914 JOURNAL OF FORESTRY 



3. Those factors which cause slowness of growth, and thus only 

 a slight increase in diameter of the axis, are accompanied by an in- 

 creased duration of the leaves. 



4. Under the same climatic conditions, those factors which cause an 

 increase in transportation are accompanied by a decrease in leaf dura- 

 tion, and thus by a decrease in the transpiring surface. 



5. Those factors which cause a decrease in photosynthetic activity 

 are accompanied by an increase in leaf duration, and thus by an in- 

 crease in the photosynthetic area. 



6. It is quite possible that the variations in leaf duration in a given 

 species may be due to differences in transpiration or photosynthetic 

 activity, caused by difference in age or habitat. 



For our nine conifers and the two evergreen angiosperm trees we 

 brief the details, giving the extremes of shortest and longest duration, 

 and below, the average of duration ; in some cases noting difference 

 of statement by other authors ; also references to position of trees and 

 pertinent remarks : 



Abies grandis.— — —\ older trees longer than saplings; shade tends to 



increase, wind to decrease duration. 



Juniperus scopnloritm. — '-: if including leaves turned brown, ^ — ^: 

 2-3 4-6 



juvenile foliage shorter duration. 



2-tS 



Picea sitchensis. ; incomplete observations ; peat and marsh situa- 



9-1 1 ' t- > f 



tion ; trees in ordinary soil not available. 



2— O 



Pinus conlorta. ^^^^-^; Sargent, 7-8; Sudworth, 6-8; mature trees 

 4-6 



longest, in contradiction to Sudworth ; saplings in open, and mature 



windswept trees shortest. 



Pinus monticola. ; mature trees longer than saplings; in peat bogs 



3-4 

 shortest of any conifer. 



Pseudotsuga taxifolia. ; Sargent and Sudworth, 8; saplings 



shorter than mature ; open much shorter than in shade ; windsweep 

 shortens, dry climate increases ; peat bog habitat increases still more, 

 at least in saplings. 



Taxtis brcvifolia. — ^^; Sargent, 4-5; Sudworth, 6-9; longer than 



supposed in densely shady position in dry climate and m ordinary 

 moisture conditions. 



