144 APPENDIX. 
infestation, but the above observations, given as definite statements, 
agree with what subsequent investigation has proved to be correct. 
We thus carry back knowledge of presence of the disease to 1869, and 
report of its presence by an observer well acquainted with it to twenty 
years before, namely, to 1849. 
Life-history.—The family of the Phytoptideg—to the genus Phytoptus 
of which the P. ribis, or Currant Bud Mite—belongs, is one of the 
divisions of the order Acarina, or Mites, but is distinguishable from 
all the other families by its more or less elongate, cylindrical, or 
worm-like shape, and also by only possessing four legs throughout its 
whole life. 
The Mites of the other families of the Acarina—as, for instance, the 
Red Spider of the Hop, the Tetranychus telarius; the Hay Mite, Tyro- 
glyphus longior; the Beetle Mite, Oribata lapidaria—are of a much 
rounder or more oval shape, but are especially distinguishable by their 
creater number of legs. As a rule, they possess three pairs when 
they are hatched and in their earliest stages, but, with subsequent 
moulis, as they approach maturity they become possessed of four pairs. 
This point of the number of legs is a very important one to ob- 
serve, in order to prevent confusion in identification with other kinds 
of Mites which may very likely be found on Currant bushes. 
The Phytoptus ribis is of the shape figured at p. 141, that is, long, 
narrow, cylindrical, somewhat tapering towards the blunt tail, at the 
extremity of which, on each side, is one long bristle, and there are 
also two other pairs of bristles one on each side of the body—one pair 
near the fore part, the other a little before the middle. The proboscis 
is short; the four legs are plainly jointed, and the abdomen with 
about seventy punctate transverse rings. The length of the female is 
0:23 millimétre, the breadth 0:04 millimétre; the dimensions of the 
male are smaller.* 
The infestation is to be found on the Black Currant (hibes nigrum) 
both in Great Britain and on the Continent of Europe. Likewise 
occasionally on the Red Currant (Ribes rubrum) and the ‘ Tasteless 
Mountain Currant” (fibes alpinum). In regard to the infestation on 
the Red Currant, the only specimens I have seen were some received 
by me on January 15th, 1888, by favour of Dr. Friedrich Thomas, of 
Ohrdruf, Gotha, well known for his researches in phyto-pathology, 
with information accompanying that he had observed them for many 
years in his own garden, but that up to date of writing no notice of 
the attack had been practically taken in Germany. 
* For practical purposes it is enough to mention that the Mites are so 
excessively small as to be indistinguishable to the naked eye. A millimétre is the 
25th part of an inch, and twenty-three hundredths of this measurement—that is, 
somewhat less than a quarter—is scarcely perceptible except when magnified. 
