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green or slightly purplish, obovate, thickish, white, hirsute, and are 

 scattered over the upper surface of the leaf, like a crop of minute 

 mushrooms. On opening them I found them hollow, without any 

 apparent inmate, or anything remarkable except a few hairs, the con- 

 tinuation apparently of a thick crop placed at their orifice in the de- 

 pression on the under side of the leaf. A few pink objects, however, 

 at length caught my attention ; and on reflection, knowing that such 

 excrescences were sometimes ascribed to mites, I resolved to ascer- 

 tain if these were not such. Next day, on shaking a few upon a slip 

 of glass, and placing them under the microscope, I observed that they 

 exhibited motion ; and some of them were not long in pushing out 

 their legs and crawling slowly about. They were all in the larva state, 

 elliptical, round-bodied, with four short legs placed close behind the 

 head ; the abdominal part is long and flexible, and has about four 

 hairs before the tip, and about as many near the shoulders. They are 

 too minute to be seen by the naked eye ; even under a triple lens, 

 they are mere linear atoms, without vestige of limbs. They are white, 

 yellow, pale brown, or pinkish. Two species of mites were found on 

 the outside : one, a yellowish rapidly running species, common upon 

 foliage, that appears to deposit its ova upon the hairs of the plants on 

 which it occurs; the other was a true, flattish, pale whitish, testaceous 

 Acarus, and is most likely the parent of the young mites in the gall. 



Knowing there were many similar galls on leaves, I next investi- 

 gated those hairy purple warts so abundant near the midrib of the 

 sloe, and found them likewise to be nests of apparently the same spe- 

 cies of A earns. 



The alternate blisters along the sides of the alder-leaf, and occa- 

 sionally found on that of the birch, gave the same result. The species 

 on the alder is probably different. The old mite accompanying them 

 is a mere point, and is well distinguished by two or three squarish 

 brown spots near the tip of the abdomen. 



The leaf of Salix aurita offers not less than four different galls : 

 one large and smooth, occasioned by a black saw-fly, (Liim. Fn. Suec. 

 2301) ; two caused by the larvae of unknown species of gall-midge, 

 [Cecidomyia) ; and a fourth minute purple one, which is very abun- 

 dant, and is analogous to those occurring on the sloe and bird-cherry. 

 The last, like them, contains only young mites. 



Another locality for mites I find in some round bud-like produc- 

 tions on the twigs of hazel. From green they become yellowish, and 

 then wither. The larva is white, as is the accompanying mite. 



A rough, pale green or purplish, fimgus-like gall, which opens 



i 



