April, ’18] 
MAXSON: PEMPHIGUS BET2E DISTRIBUTION 
235 
cent while of those in the east half where there are but 22 narrow-leafed 
trees, 65.96 per cent have a like infestation. 
In the north half of this territory there are 156 narrow-leafed cotton¬ 
wood trees and in the south half 437. Of the fields in these halves 
78.6 per cent of those in the north and 84.6 per cent of those in the 
south half have an infestation of over 70 per cent. 
If we compare all fields within one-half mile of narrow-leafed trees 
with all those from one-half to three-fourths and all over three-fourths 
mile of these trees we find 78.57 per cent, 60 per cent and 54.76 per cent 
respectively of the fields in the three zones have an infestation of over 
80 per cent. 
In making similar comparisons in the Eaton territory we find the 
same higher degree of infestation in fields within one-half mile of nar¬ 
row-leafed cottonwood trees. 
We also find that the western halves of both the north and south 
sections of this territory carry a heavier infestation than the eastern 
halves. In these sections it cannot be due to trees within the terri¬ 
tories, as the northern section is nearly treeless and contains but one 
narrow-leafed cottonwood which is near the southwest corner of the 
section. 
The south section has 46 trees of this species, 41 of which are in the 
southwest corner and five near the southeast corner. When the 
survey was made no galls of Pemphigus hetee were found on any of 
these trees, most of which w r ere small second growth stock or sprouts 
coming up about stumps of larger trees which had been cut down the 
year previous. 
The heavy infestation of the west as compared with the eastern 
portion of these sections suggests the effect of the wind which is no 
doubt an active factor in the dissemination of the beet root-louse. Just 
how far the beet root-louse is carried by the wind has not been deter¬ 
mined. During early summer, while the heaviest migration of this 
insect from the winter host is taking place, the prevailing winds of 
northern Colorado are westerly. It does not seem unreasonable that 
these insects might easily be carried from*the mountains, many miles 
out on to the prairies by these winds. 
West of the northern section of the Eaton territory there are several 
miles of practically treeless, unirrigated land. The Cache La Poudre 
River passes just southwest of the southern section of this territory. 
Along this stream there is a timber belt of varying width within which 
there are some narrow-leafed cottonwoods. It is probable that the 
infestation of the Eaton territory comes largely from these trees if not 
from the mountains. 
This survey has been continued during the present summer in the 
