140 
Adults of this mite measure from .005 to .0005 inch in length, 
with the greatest transverse diameter about .002 inch. They are 
whitish and semi-transparent. Oi the three pairs of hairs attached 
to the dorsal surface, the first pair is attached at the posterior mar¬ 
gin of the cephalothorax, the second between the last two abdominal 
striae just before the terminal sucker, and between the hairs of this 
pair is the third pair, consisting of two short and straight hairs. 
The hairs of the second pair are abruptly bent at about the fourth 
of their length from the attachment. The first of the three ventral 
pairs of hairs is twelve, and the second twenty-four, striae behind 
the cephalothorax; the third pair is attached six striae in advance 
of the terminal sucker. The legs are strongly compressed, project 
downwards, and the feather-like tarsal appendage bears five pairs of 
prongs. The striae of the abdomen number about 80. 
In the latter part of the summer of 1880 my attention was called 
by Prof. S. A. Forbes to the diseased condition of arbor vitae 
hedges in and about Normal, Illinois, and upon searching the trees, 
this Phytoptus was found creeping about the leaves. I was inclined 
at the time to refer the condition of the hedges to injuries inflicted 
by the mites earlier in the season; for they were not sufficiently 
abundant at the time the examination was made to cause serious in¬ 
convenience to the plants. Since then the trees have regained their 
usual, thrifty appearance, and the mites, although still present on them 
at all times of the year, have not been more abundant at any time 
than they were when first discovered. The Phytoptus of _ the arbor 
vitoe spends the winter in the buds and under the margins of the 
leaves. It can be secured in midwinter by bringing infested twigs 
into a warm room. 
Phytoptus pyrif Scheuten. 
The interesting observations on this and the following mite are 
from the pen of Prof. T. J. Burrill. 
Invisible to the naked eye. Under the microscope, white or with 
transmitted light, brown. Nearly cylindrical. Varying in size. The 
largest mites measure .19 mm. in length and .05 mm. in diameter. 
Transverse striae 50-80.—Sorauer. 
“In the spring of the year the leaves of the pear tree as they un¬ 
fold from the bud, are often studded with small red spots which, 
upon closer looking, are also seen to be slightly thickened areas of 
the leaf. The red soon changes to a brown color, indicative of the 
death of the cells and tissues of the affected spot. When very 
numerous, as these spots often are, they coalesce, forming patches 
of various sizes, not unfrequently covering large areas of the leaf, 
in which case the leaf usually prematurely falls. The common 
name, pear-leaf blister, has been not inappropriately given to the dis¬ 
ease. The cause of the difficulty is the above-named mite, origin¬ 
ally known only in Europe where it was discovered and named 
Typhlodromns pyri by the German naturalist, Scheuten. It was, 
however, introduced into our country many years since, having no 
doubt been brought over with pear trees, of which the importations 
have sometimes been large. There are many localities with us now 
where no signs of the disease are to be found, but the pest is very 
