38 
ON THE DISEASES OF PLANTS. 
of roots, many trees remain apparently stationary in growth for a time ; they are 
engaged, however, in forming roots according to the loss sustained. 
The operation of cutting or laying bare roots of trees to force them to become 
fruitful is only an apparent exception to the foregoing remarks ; for the production 
of fruit in such cases must be considered as the first step towards decay, it depend- 
ing not so much on a full supply of nourishment as on a state of maturity necessary 
for the purpose. 
Treatment. — When the roots have been attacked by insects endeavour to destroy 
them. The most approved solution is lime water and tobacco water poured upon 
the ground over the affected parts ; even unslacked lime has been dug in with 
advantage. To entrap the wireworm (Elater segetis) Sir Joseph Banks recommends 
slices of potatoes to be buried where they abound, frequently examining the baits, 
and destroying such as have collected on them. When a plant happens to have its 
roots lacerated, these ought to be protected from extremes of heat and cold ; the 
ground in the neighbourhood should be kept moderately moist ; if possible, the 
plant itself shaded, and whatever else may be found conducive to its health should 
be resorted to, to induce the formation of new roots. 
Gangrene of Roots. — This occurs often, and is of two kinds — wet and dry gan- 
grene. An example of the first kind occurs frequently from too much moisture, 
accompanied with cold weather and a bad soil, or in consequence of the succulent 
nature of the parts in which it occurs. It is frequently found in " house plants/' 
when these have been officiously indulged with too much water. Dry gangrene in 
roots is similar to that in the stems, and is noticed under that head. 
Lacerated and incised wounds of Leaves. — These occur from the attacks of 
animals, chiefly of the insect tribes ; from hail ; and many of the lower animals are 
very destructive to the leaves whilst feeding. Some birds seem to do so for amuse- 
ment. The Apis centuncularis cuts out portions of leaves, and carries them away 
for its use. Plants frequently become stripped of the foliage in a short time by the 
ravages of the caterpillars, of butterflies, and moths, although, generally, these are 
more sparing in their attacks. These, with many others, attack most plants fit for 
the food of man. 
Various methods have been had recourse to, for the destruction of caterpillars ; 
washing with tobacco- water and soap, lime-water, &c. : boiling water has also been 
tried with success ; for those insects which seek the ground at particular seasons, 
unslaked lime laid on and dug in is advantageous. 
There is what may be termed an approach to a natural cure for this infection, 
in the larvae of an aphidivorous fly which is described and represented by Darwin. 
The same animal also destroys the caterpillars in great numbers. 
Remarks of Mr. Elliott on the subject, — When the foliage is all off the trees and 
bushes, wash them over with the hand-engine to clear them of decayed leaves ; for 
this purpose any water will do : then stir up the surface of the earth all round 
their roots, and lay a little hot lime about them to destroy their eggs. 
Hail is a frequent cause of wounds in leaves, and to ward off these destructive 
showers, " pafagreles " have been used on the Continent. The most approved kind 
