392 



ECOLOG Y. 



effect, probably, in causing many of the young spruces over the 

 center of the formation to die off. 



706. This may also have been hastened by fires which would 

 now more often sweep over the swamp during dry seasons. In 

 partial evidence of this are many young spruce trees with scars 

 near the ground where the bark has been destroyed. This gives 

 admittance to wood-boring insects which farther aid in the proc- 



Fig. 487- 

 Dying black spruce in moor. (Photograph by the author.) 



ess of weakening and debilitating the trees. The dying off of 

 the lower limbs of these marsh spruces suggests both the action 

 of fire, as well as excessive moisture at times. Many of them 

 now present only a small convex top of living branches. It is 

 interesting to observe the gradation in this respect in different 

 trees. 



707. The weird aspect presented by a clump of these dying 

 young spruce trees is heightened also by the changes in the form 

 of the branches as they die. The living branches have a graceful 

 sigmoid sweep with their free ends curving upwards as in many 



