The leaves of plants frequently assume an unnatural form on account of their being wounded by insects. Keith, in his Physiology of Plants, thus enumerates some of the most customary: -

"The leaves of the apricot, peach and nectarine are extremely liable to be thus affected in the months of June and July. The leaf that has been punctured soon begins to assume a rough and wrinkled figure, and a reddish and scrofulous appearance, particularly on the upper surface; the margins roll inwards on the under side, and inclose the eggs, which are scattered irregularly on the surface, giving it a blackish and granular appearance, but without materially injuring its health.

"In the vine the substance deposited on the leaf is whitish, giving the under surface a sort of frosted appearance, but not occasioning the red and scrofulous aspect of the upper surface of the leaf of the nectarine.

"In the poplar the eggs, when first deposited, resemble a number of small and hoary vesicles, containing a sort of clear and colourless fluid. The leaf then becomes reflected and condupli-cate, inclosing the eggs, with a few reddish protuberances on the upper surface. The embryo is nourished by this fluid, and the hoariness is converted into a fine cottony down, which for some time envelops the young fly.

"The leaf of the lime-tree, in particular, is liable to attacks from insects when fully expanded; and hence the gnawed appearance it so often exhibits. The injury seems to be occasioned by some species of puceron depositing its eggs in the parenchyma, generally about the angles that branch off from the midrib. A sort of down is produced, at first green and afterwards hoary, sometimes in patches, and sometimes pervading the whole leaf, as in the case of the vine. Under this covering the egg is hatched; and then the young insect gnaws and injures the leaf, leaving a hole or scar of a burnt or singed appearance.

"Sometimes the upper surface of the leaf is covered with clusters of wartlike substances. They seem to be occasioned by means of a puncture made on the under surface, in which a number of openings are discoverable, penetrating into the warts, which are hollow and villous within".

For these the only remedy is to remove the insects with the least possible delay; and, if the injury is extensive, adding water and liquid manure to the roots rather more freely, to promote a fresh and larger development of the leaves.

Deformities of the stems of trees and shrubs arise from another cause - from the extension of the woody fibre being greater and longer continued on one side, it frequently becomes contorted. Gardeners usually endeavour to remedy this by making an incision on the inner side of the curvature, and then employing force to restore it to a rectilinear form, causing a gaping wound, and mostly failing to attain the object. If the incision be made on the outer side of the curve, thus dividing the woody fibres that continue to elongate most rapidly, the branch or 6tem, with but slight assistance, will recover its due form, and there will be no open wound.

"From the fact that there is invariably more woody matter deposited on the side of a stem or branch which is most exposed to the air and light, gardeners have explained to them why those sides of their trained trees which are nearest the wall ripen, as they term it, most slowly, and are benefitted by being loosened from the wall so soon as they are relieved from their fruit.

"If they require any demonstration that this explanation is correct, they need only examine the trees in clumps and avenues: their external sides will be found to enlarge much more rapidly than their internal or most shaded sides." - Principles of Gard.