124 LEAF-HOPPERS. 
tar and, lying flat on the lawn, was dragged along by means of 
three cords, one fastened at each end, and one in the center. 
The advantage of this form of machine over the preceding was 
at once apparent. It was more easily operated, no tar was wasted, 
and the insects upon springing into the air were almost certain 
to fall upon it in their descent. Two plats of blue grass upon 
the college lawn, having as nearly as possible the same natural 
advantages, were selected for experiment. May 29th one of 
these plats, which for convenience we will call plat I, was run 
over with the dozer, letting it at each round of the plat run over 
about half its width on the track of the preceding round, so that 
the entire plat was run over twice with the dozer. This plat, a 
triangle, was bordered by a grape patch on one side, and by 
roadways about twelve feet wide on the other sides, so that the 
migration of the leaf-hoppers into it from adjacent parts was in 
some degree prevented. The second plat, directly adjoining, was 
left untouched, and in this the insects pursued their work. The 
difference in growth and vigor of grass on the two plats was 
very noticeable in a short time, though no advantage of one over 
the other could be detected at the beginning of the experiment. 
This difference was more marked during an extended dry period 
than at any other time, thus indicating that the grass upon the 
untreated plat was materially sapped by the insects. Any possi- 
ble natural advantage which plat I may have had over plat II 
we think insufficient for all the difference noticed. In order to 
ascertain the comparative numbers of insects at work in the 
plats, on the ninth of June, the dozer was dragged three rods 
on plat I. By actual count three hundred leaf-hoppers were 
taken. On plat IJ, in moving the dozer the same distance, 1,564 
leaf-hoppers were taken; that is, more than five times as many 
as upon the plat which had been treated ten days previously. 
Upon the same day we attempted to clear plat I the second time 
with the dozer, but were compelled to stop by the interference 
of the grass pollen which soon covered the tar and enabled the 
insects to leap from the dozer back into the grass again. Hence, 
the dozer must be used before the grass blossoms, if grass is 
allowed to go to seed. On the twentieth day of June we again 
tried the dozer, the insects at this time for the most part being 
well developed and able to fly. Two men operated the dozer, 
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