592 ADDITIONAL NOTES,

by the aphis; as leaves of the nut-trees in my garden on the banks of the Derwent are every year crowded with innumerable aphifes on their inferior furfaces, and yet I have feen few, if any of them, on nut-trees in fome higher fituations, which I happened to infpeët. Add to this, that the great honey-dew, mentioned in Seét. XIV. r. 7. was produced on a row of willows by the fide of water. This may neverthelefs be in part afcribed to fome other local circumftance; as I this year obferved numerous large black aphides round the ftalks of garden-beans on a clayey foil, which did not exift in my garden, which may be called a carbonic foil. Though on the peach and nec- tarine trees, againit the walls in my low garden, and on fome plum- trees, the aphides exift almoft every year in fuch deftruétive mul- titudes as to prevent the fruit from fucceeding, and thence to render them not worth cultivation; and to render the leaves of the nut- trees lefs in fize, and lefs prolific than other nut-trees on a more ele- vated and clayey foil, with which I this year compared them.

Why the aphis fhould be fo much more numerous in moift fitua- tions is a curious fubject of inquiry, but is fo fimilar to another ani- mal fa&, that they may illuftrate each other."The cough and con- fequent confumption of fheep, which occurs annually in moift fitua- tions, is owing to an infect called a fleuk-worm, about the fize and fhape of a child’s finger-nail, which creeps up the gall-duéts from the inteftines, and preys upon the livers of fheep; as may be feen in moift feafons in our fhambles.. This feems to occur from the bile becoming too dilute from fo much watery nourifhment in thofe ani- mals, and that thence it does not poñlefs fufficient bitternefs or acri- mony to prevent the depredation of thefe infeëts, as in drier feafons. On'the fame account I fufpeét the juices of nut-trees and of willows planted in very moift fituations may be rendered too dilute; but that in higher fituations they may poñlefs fufficient acrimony or bitternefs

mixed with the fap-juice to prevent the depredations of the: aphis.

See Sect, XIV. 2,8. 6. To