248 REPORT OF THE No. 3 



It may extend indefinitely towards the tip of the branch, commonly for not 

 more than half an inch, but sometimes for several inches. Occasionally the 

 leader is destroyed in the same way as the branches. 



The wound in itself is not sufBcient to cause the death of the branch. This 

 was proved by similarly removing the bark with a knife from healthy branches in 

 July of 1919. The wounds healed before the end of the season, and they have 

 shown no ill effects of their maltreatment since then. But when the wounding 

 takes place so late in the season that there is no time left for covering the edges 

 of the wounds with new tissues the result is different. Twenty-five branches 

 were wounded in the same manner in October, 1919. Without exception every 

 one of these branches died from the point of wounding outward and their foliage 

 was red by the following May. 



The cause of the wounding in most cases is the large bark beetle Mono- 

 hamus scutellatus. It would also appear from experiments that the rarer 

 M. marmorator exhibit the same habit — a habit of these beetles not before 

 known; indeed, it is altogether probable that other species of Monohamus 

 {Monochamus) resort at times to bark-chewing. 



A few instances of what appear to be snow pressure or fungus action occur 

 at times, but in such cases the bark remains intact. Likewise, there are instances 

 of removal of the bark by rubbing, or of the pulling off of low-placed twigs or 

 small branches in the fall or winter, followed by the death of the branches, but 

 they are not frequent. So, too, branches are sometimes killed by breakage 

 due to wind or sleet, or insect burrowing. But the prevalent cause of "red 

 branch" is the combination referred to above. 



Now what is true of balsam is also true of white pine (Pinus strohiis), red 

 pine (P. resinosa), jack pine (P. banksiana), arbor vitae {Thuja occidentalis) , 

 black spruce (Picea mariana) and white spruce (P. canadensis). In the case of 

 the spruces there is an early defoliation and naked branches appear as bushy 

 spikes — hence the term "spike branch." Dr. Craighead reports that at Bathurst, 

 N.B., about 50 per cent, of the "spruce trees standing in old logging operations 

 were defoliated by M. scutellatus feeding on the under side of twigs." 



In proof of the statement that Monohamus is the cause of the wounding 

 Dr. Craighead deposited two males of M. marmorator and two females in a cage 

 placed over a living balsam tree six feet high on July 7th. On August 24th 

 much gnawing on the under side of the branches was noted, and by September 

 15th nearly all of the branchlets had been wounded in this way. By. the follow- 

 ing spring twenty-one branches had died and reddened. A similar experiment 

 was carried out with M. scutellatus and with like results. 



2. Butt and Heart Rots. 



(a) General. — A distinction is drawn between butt and heart rots. The 

 former are rots of any kind localized in the lower part of the trunk and the ad- 

 joining roots of a living tree; such rots commonly begin in the roots at the base 

 of the trunk and work their way upwards. The heart rots occur in the heart- 

 wood of the main trunk; they commonly enter by way of knots or wounds. 

 Fundamentally there is no difference between the two kinds. Both are caused 

 by fungi. Delicate fungal threads, visible only with the aid of a microscope, 

 except where they form sheets or strands, penetrate the wood partially digesting 

 it; the undigested remains constitute the "rotted" wood. Fruit bodies, usually 

 in the form of brackets or punks (but in a few species as mushrooms or toadstools) 

 eventually develop on the surface of the diseased parts, but as a rule only after 



