The Phytoptus of the Vine. By Prof. Giovanni Briosi. 185 
explains by a partial diminution of the intercellular pressure, in the 
wounded and emptied cells, and Sorauer * by a hardening and 
perhaps a cuticularization of the cells due to the action of the 
atmosphere, which penetrates into the structure of the wounded 
cells. Now, without wishing to set these causes entirely aside, I 
think that the same forces which produce the hairs also cause this 
phenomenon. In fact, the afflux of the substance which takes 
place towards that spot of the leaf, where a gall begins to be 
formed, must extend by endosmosis and exosmosis more or less 
to all the strata of the texture lying in the thickness of the leaf, 
thus offering to all the cells of the lamina in the region correspond- 
ing with the wounded spot a more than usual nourishment. Whilst 
therefore the cells of the under side of the leaf discharge so much 
material, owing to the hair production, those underlying, up to the 
epidermis growth of the upper side, participating in this increased 
nourishment must of course grow and swell, which they (to my 
mind at least) cannot do without producing an incurvement of the 
lamina of the leaf, since the texture which compasses the gall in 
its normal state cannot grow with the same force and rapidity on 
account of the lesser nourishment. 
We now come to the mite, or acarus, the cause of the disease, 
This animal, belonging to the species Phytoptus Dujardin 
(Phytoptus vitis, Landois), is invisible to the naked eye, and its 
extreme smallness renders the study of the same, even with the 
microscope, most difficult. This explains why, notwithstanding 
the most painstaking researches of distinguished scientific men, 
there is still some doubt about its formation. The body is long, 
flexible, almost cylindrical, tapering off at the two extremitiés, 
which are slightly inclined towards the belly (Figs. 2, 3, 11, 12). 
In front it has two pairs of legs, which, when extended, project 
a little (about 0°01 mm.) beyond the extremity of the head. It 
is covered with transversal rings, which extend on one side to the 
insertion of the hinder pair of legs, and on the other to within 
a short distance of the anal opening. The cephalo-thoracic region 
is smooth, viz. without rings, whilst a very small depression, which, 
however, can always be distinctly recognized, separates it from 
the abdominal region. Above, nothing distinguishes the head from 
the thorax (which is common indeed to all arachnida, they having 
a cephalo-thorax), one superficies continues on both the segments, 
and the front part, which is turned down, terminates in a conical 
trunk. 
The proboscis communicating with the head is hollow, open in 
front (Fig. 12, m), and behind terminating at the cesophagus 
(Fig. 5, 2). On the abdominal side, that is, the one opposite to 
the dorsal, this cavity opens longitudinally, and shows an almost 
* Handbuch der Pflanzenkrankheiten, p. 171. 
