EXTRACTS — HORTICULTURE. 
639 
appears to be fumigation with tobacco-smoke, followed up by washing with lime- 
water, aud finishing by digging the ground around the plants. Leaves are fre- 
quently found traversed by white lines, twisting and running in all directions, — 
they are caused by the larvag of certain insects, which eat their way through, 
leaving their excrements behind them in their paths ; and so neatly do they per- 
form their works of destruction, that by far the finest dissection we have ever 
seen, were the works of some of these animals. They burrow under the cuticle, 
and generally confine themselves to the upper surface of the leaf, sometimes to 
the lower, occasionally however both are attacked ; such we have observed in the 
leaves of many plants, aud believe it to be in consequence of the larva; piercing 
the leaves. Some insects lay their eggs close to each other on the back of the 
leaves of certain plants. After a time these become hatched, aud the larvae, 
each for itself, jjierces a small hole immediately above the attachment of the egg 
from which it came, and passing through the leaf, arrives at the upper surface, 
where it commences its mining, covered outy by the cuticle ; these do not tra- 
verse the leaves like the others, but confine themselves to one part. The leaves 
of apple and pear trees are very subject to this affection. The treatment of such 
is not as for the Aphis, in consequence of the protection they receive from the 
cuticle. The most powerful remedy is boiling water. 
Wounds of Leaves with Oviposition. The most curious effects produced 
by the wounds of insects, are the various kinds of galls. These are tumours 
produced on various succulent surfaces, varying according to the insects which 
effect them, or the plants in which they occur. They are caused by insects of 
the order Hymeuoptera and Genus Cynips, and occur in a variety of plants, but 
most frequently in the oak aud willow. — It is very evident, that these various 
excrescences must materially injure the health of the plants on which they occur, 
from the inordinate consumption of substance required for their nourishment ; 
and this is found to be the case, for when they occur in great numbers, from the 
excess of nourishment drawn off, the branch, or even the whole plant suffers, the 
leaves become distorted and small, and the whole plant stunted in growth. They 
scarcelj' admit of a cure in many plants. The method we would recommend in 
the early stage, is the application of boiling water ; afterwards, when of O'^^- 
derable size, nothing but their removal will be of service. — 
Parasitical Plants on Leaves. Leaves are liable to become attacked by 
various cryptogamia plants, from circumstances not well ascertained. The most 
familiar of these diseases is known by the name of "Mildew" (Sporotrichum 
macrosporum ;) certain circumstances seem particularly favourable to its appear- 
ance, as cold drj' weather, aud particular exposures ; plants under the shade of 
others, or othenvise shaded, apparently suffering more than those fully exposed. 
From microscopical observation, this parasitical plant, constituting " Mihhtv" 
seems to be composed of globular semi-transparent masses, apparently some- 
times attached to a stalk, sometimes to hairs on the plant, or collected into 
heaps on the surface of leaves and stems. — Amongst the remedies proposed, per- 
haps the best is thinning around the affected part, or removing to more light 
and air. Delicate and rare plants may have their leaves washed \vith water. 
We have found lime-water of service on apple trees. In hardy plants slightly 
affected, remove all the diseased leaves or shoots, and attend to the other circum- 
stances mentioned. An apple-tree annually affected, was perfectly cured by a 
free washing of what is termed the " cream of lime," durinfr the winter; from 
4 K .3 
