THE SPRUCE INVESTIGATION. 235 



reference was had to the timber that died in 1892, or that 

 which had not recovered from the injury sustained during that 

 year. 



Thus, we have a fairly complete history of the progress of 

 the two apparently distinct troubles which caused the death of 

 an enormous amount of spruce timber. The one starting in 

 1882, and continuing until about 1886, the other starling in 

 1890-91 and ending in 1893. 



CAUSE OF THE FIRST TROUBLE. 



The origion and cause of the unhealthy condition of the 

 spruce during the period between 1882 and 1886 cannot be ac- 

 curately determined, since no investigations were made during 

 its progiess, but from such evidence as could be obtained from 

 the dead timber, and the existing conditions at the time of the 

 fiist investigation in 1890, and a study of the habits of the 

 various insects found in the bark of living and dying trees, to 

 the present time, it appears that it must have been caused by 

 insects. 



The facts obtained in 1890, as recorded in Bulletin 17, seemed 

 to warrant the conclusion that the destructive spruce bark 

 beetle 1 was the prime cause of the death of the trees, and that 

 the trouble had been brought to an end by the influence of its 

 parasites. The results of subsequent observations, however, 

 have not fumished additional evidence that this would be a 

 correct conlcusion. In fact, while I have frequently found the 

 adult, eggs, and young of the spruce bark beetle in the living 

 bark of injured or dying trees and recently cut logs, 1 have not, 

 as yet, found it in the bark of a healthy vigorous tree. This 

 failure to find it in the bark of healthy trees may be due, how- 

 ever, to its preference for the bark of injured and 

 recently felled trees, and that, the abundance of the latter in 

 different sections of the forest since 18S5, has rendered it uri- 

 neccessary that they should attack healthy trees; and in this 

 might be found an explanation of the ending of the trouble in 

 1886, since the increased cutting of timber in the northern as 



1. Polygraphus ruftpennis. 



