October, '16] QUAYLE: SCALE DLSPERSIOX 491 



row on the south side shows 5,128 scales as against 1,427, or a difference 

 of 3,701 on the fifth row from the infested trees. Taking the first row 

 on the west again, there is a total of 2,218 scales on the 25 leaves on the 

 west side of every fifth tree, as against but 369 scales on the same num- 

 ber of leaves on the east side of the same trees. The prevailing direc- 

 tion of the wind, it will be noted, was from the southwest. 



This four-acre block, as the results have shown, was not large enough 

 to determine all the possibilities of the experiment. It was scarcely 

 anticipated that the scales would have spread over the entire area in 

 one season, and since the infested trees were on three sides with a 

 slight wind blowing from the opposite direction at night, as compared 

 with that of the day, there appears to have been some movement 

 from this direction. However, on the east row of the block, immedi- 

 ately adjoining infested trees, there are more scales on the west side 

 of the trees than on the east side. The figures are 1,020 for the west 

 side and 388 for the east side. With a few exceptions, all of the trees 

 show more scales on the west than on the east side of the tree. On tree 

 13 in row 1, for example, 660 scales are found on the 25 leaves on the 

 west side as against 36 scales on the same number of leaves on the east 

 side. 



From a practical point of view the agency of the wind in spreading 

 jjlant-feeding or disease-bearing insects is of very great consequence. 

 In the case of the block of trees referred to, the work of fumigation 

 in 1914 was so satisfactory that the trees should have gone several 

 years without treatment. As it was, in spite of the fact that 100 per 

 cent of the scales were killed, the trees could not go untreated over a 

 single year and had to be fumigated in 1915. Other host plants grow- 

 ing in the vicinity, particularly border host trees, are, likewise, directly 

 responsible for reinfesting treated trees. 



During the present season we varied our experiments on wind dis- 

 persal somewhat by having more direct control of the origin of spread. 

 This was done by cutting branches, badly infested with the black scale, 

 and suspending them on a pole in the midst of barren ground. Three 

 tanglefoot sheets were placed in the form of arcs of circles at distances 

 of 26, 46, and 70 yards respectively on the leeward side of the in- 

 fested branches. The length of the inner arc was about 15 yards and 

 of the outer arc about 45 yards. Three sheets were also placed on the 

 windward side at a distance of 15 yards from the infested branches. A 

 total of 60 young black scales were captured on the nine sheets on the 

 leeward side, and none on the three sheets on the windward side. The 

 maximum number on a single sheet, 24, was found on the one directly 

 in front of the point of origin. The total of the three sheets in this 

 arc, a distance of 26 yards, was 37 scales. The total on the next three 



