. Bulletin of the Department of Agriculture. Agriculture. THE WESTERN GRASS-STEM SAWELY. 15 If the same amount of moisture had entered the stem where the larva was hibernating it probably would have caused its death. This experiment, taken in connection with others that were not so directly conclusive, seems to prove that the porous plug in the stub must prevent in some way the admission of an undue amount of moisture into the chamber below, although water readily penetrates it. The gallery below the plug is always entirely free from debris, forming a hibernation chamber and later a pupat
. Bulletin of the Department of Agriculture. Agriculture. THE WESTERN GRASS-STEM SAWELY. 15 If the same amount of moisture had entered the stem where the larva was hibernating it probably would have caused its death. This experiment, taken in connection with others that were not so directly conclusive, seems to prove that the porous plug in the stub must prevent in some way the admission of an undue amount of moisture into the chamber below, although water readily penetrates it. The gallery below the plug is always entirely free from debris, forming a hibernation chamber and later a pupation cell. Within this chamber the larva lies with its head up and usually pressed against the barrier at the top, always on the alert to retreat down- ward at any sign of disturbance. It descends l)y alternately flexing and straightening the body, bracing itself first by the jaws, then by the caudal horn as it hitches its way down In ascending, the caud'?J horn is thrust against the side of the gallery or the cocoon, the body is straightened, the jaws obtain a pur- chase to hold the dis- tance gained, when the body is again drawn up until the caudal horn is applied to the side wall for another push. Late in the summer or during the autumn the larva spins for it- self within the hiber- nation chamber an almost transparent tube of filmy silken tissue. This silk tube is sometimes several times the length of the larva, is closed at both ends, and is free from the sides of the chamber, so that often it can be readily withdrawn entire. When first constructed this fabric is comparatively strong and pliant but after some months it grows more brittle and is easily ruptured. As a rule it remains intact until the emergence of the adult. Even the presence of half a score of parasitic larvae often fails to wreck the deli- cate structure during the winter. The longevity of the sawfiy larvae is remarkable and is worthy of mention. September 8, 1911, a number of stubs of Elymus conden- satus c
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