48 MICHIGAN ACADEMY OF SCIENCE. 



iug on the bark were several small openings, less in diameter than a 

 pin. From these openings burrows were traced. The burrows are 

 at first A^ery small and lie close under the bark and are filled with dark 

 granules, probably colored by tannin. As they become larger and 

 begin to run deeper, thej are tilled with a whitish dust shown by the 

 microscope to be parts and groups of wood cells. 



As to extent one was followed through its winding course a dis- 

 tance of 1 foot 7 inches in a length of branch of 4 inche.s, now near 

 the bark, now deep down in the wood; now running upwards in the 

 branch, now running downwards. Neither the beginning nor the end 

 of this burrow was found. The branch was somewhat less than an inch 

 in diameter. As mentioned above in small branches the course be- 

 comes straight. One buriow was traced upwards in a branch of about a 

 half inch in diameter a distance of about eighteen inches, then doubling 

 upon itself ran downwards parallel to the upward course When the 

 branch becomes a fourth of an inch or so in diameter no doubling is 

 l»ossible and chambers are often found hollowed out in such twigs. The 

 wood for some distance around a burrow is often found ^discolored and 

 decaying thus weakening the branch and producing the breaking men- 

 tioned above. This breaking often takes place at a chamber, expos- 

 ing the larvte to cold and to birds. Woodpeckers are in the habit of 

 burrowing down to the chambers and extracting the larvae. 



When the beetles leave the trees they leave a hole which in outline 

 has one straight side and one curved. The back of the insect in com- 

 ing out is turned towards the curved side. Either side may be upwards 

 or downwards on the tree, but always one or the other. These holes 

 may be very numerous on one tree. Eleven were counted, in one in- 

 stance, on a circular space of two and one-half inches in diameter. 



Although the beetles may be coming out in numbers, few are found 

 upon the tree. They seem to crawl about for a short time and then 

 taking flight leave the tree. 



Methods of destruction were thought of but are hard to apply, on 

 account of this Imbit of leaving the tree, and besides it was found 

 that they do not feed upon the leaves of the birch. This was demon- 

 strated by keeping a number in a large glass jar in the laboratory' and 

 supplying them with fresh leaves. When only birch leaves were sup- 

 jjlied they fed but very sparingly. Some elm leaves were then put in 

 with the birch and they fed greedily upon these. This led to further 

 experiment and various sorts of leaves were used. They fed upon 

 almost any leaf of a soft texture. But their favorite food was willow, 

 poplar, and aspen leaves with preference strongly marked in the order 

 given. 



It seems from tliis that the beetles upon leaving the birch feed on 

 other trees until the time for reproduction. 



Peculiar growths in the tree itself are caused by the burrows, or 

 rather by some stimulus furnished by the burrows or by the larvae. It 

 was stated that wherever the burrows were near the cambium corre- 

 sponding ridges were to be found on the outer surface of the bark. This 

 is due to a growth of sclerotic cells which is formed as an arch over the 

 burrow on the side towards the bark. When the burrow is entirely 

 below the cambium no such growth occurs. It appears that the cam- 



