1912.] PUBLIC DOCUMENT — No. 31. 21 



vine growth must have an important hearing on the efficacy of 

 both flowing and sj^raying treatments. In practice, it seems to be an 

 easy matter, on a thinly vined bog, to control this insect sufficiently to 

 keep it from doing serious injury, either by spraying with arsenate 

 of lead or by flowing, while it is apparently impossible to prevent 

 serious injury on a densely vined bog by either of these treatments. 

 The control of this insect, therefore, seems to hinge on the acquirement 

 and maintenance of a thin vine growth, which is also the most de- 

 sirable condition for maximum crops. Unfortunately, it seems difficult 

 to get a thin vine growth on some bogs. However, this can probably 

 be readily accomplished in most cases, at least, by heavy sanding and 

 proper adjustment of Avater conditions. This adjustment might be 

 along either or both of the following distinct lines : — 



1. Early withdrawal of winter flowage with no long-continued re- 

 flowage. 



2. Sufficient drainage. 



Experiments to test the methods of controlling this insect, here 

 suggested, have already been started. Observations seem to show that 

 large bogs, when compact {i.e., approaching a circle or square) in 

 general form, are, other conditions being the same, much more troubled 

 with this insect than are small ones. Probably the chief reason for 

 this is the fact that, during the summer, pai'asitic and predacious in- 

 sects and spiders do not become so thoroughly distributed over the 

 large bogs, at least until the periods of fire-worm activity are nearly 

 over, and so do not become to so great an extent a controlling factor. 

 On a winter-flowed bog, most of these foi*ms are probably either de- 

 stroyed or driven ashore bj^ the flooding every year. They should not, 

 during the summer, become as uniformly distributed on a large, com- 

 pact bog as on a small one for two reasons, viz. : — 



1. The distance which the parasitic and predacious forms must go 

 to reach the central portion of the bog is, of course, greater on a large 

 bog. 



2. As the area frorii which these fomis come onto the bog is prob- 

 ably restricted, for the most part, to a fringe at most only a few hun- 

 dred feet wide, the area of the bog as it increases in size, if it is com- 

 pact in shape, increases out of proportion to the increase of the area 

 of this fringe. This argument agrees well with the following pre- 

 viously reported observations : — 



1. The fire worm is only very rarely, if ever, troublesome on strictly 

 dry bogs in Massachusetts. 



2. When a winter-flowed bog becomes infested the infestation first 

 noticed is always some distance away from the upland, usually where 

 the winter flowage is deep. 



The fact that, on a comjiact bog, there is a larger acreage within a 

 given distance of any point, up to a distance that would take in the 



