290 
ON THE MILDEW OF PI ANTS. 
former, and on the following morning each leaf was perceived to be 
hilled, and rendered brown. Thus it is apparent that either carbonate 
of soda, or the pure alkali in a very diluted state, will destroy leaves 
entirely ! Whether the latent buds on the twigs will sprout or not, 
is a point to be ascertained. 
A liquid sulphuret of lime , made by boiling an ounce of sulphur in 
a gallon of water, and adding to the hot fluid about twice the quantity 
(two ounces) of lime, being used cold, did not injure apple leaves; but 
it has not yet appeared certain that the mildew will yield to it. I may 
here remark that this solution is of a yellowish colour, of a powerful 
taste, and sufficiently strong for many purposes: it cannot be used 
with safety to melon plants ; but I believe it to be very efficacious where 
the vine is infested with the red spider, or the pine with the crocus. 
If a tea-spoonful of Gallipoli, linseed, or train oil, be put into a phial 
with one or two tea-spoonfuls of soft water, and as much caustic soda 
liquor be added as will combine with it in the form of a white (soapy) 
emulsion, a plant may be anointed (rose, apple, pea, bean, strawberry, 
and what not) without material injury : a spottiness, however, will be 
created, and in the instance of the pea leaf, that peculiar glaucous 
marbling, which, I think, originates in an insect—as I have found one 
under the epidermis of the lower side, under those marks—appear 
to be affected by the fluid, and to become discoloured. Oil alone, in 
fact, will affect a leaf, and produce discoloration ; it will also, beyond a 
doubt, destroy the mosses and lichens upon the stems of fruit trees, 
as I have proved and witnessed in the Isle of Thanet, where the dwarf 
standards are often kept clean by train oil. But the application of this 
substance is not advisable upon foliage, as the pores {stomata) of leaves 
must thereby be greatly clogged. 
After all that I have observed, I arrive at the conclusion, that oil or 
soda—the chemical ingredients of soap—are efficient applications, in as 
much as they may destroy a fungus, but that they are each improper 
agents, and cannot be used with safety to a plant ; that the chemical 
compound termed soap, is one wherein the peculiar qualities of each 
ingredient is electro-chemically neutralised by the energy of each acting 
the one upon the other ; and that soap, the product, is the only 
form in which soda, potassa, or oil, can prudently be applied to the 
leaves of plants. 
I repeat, that my experience does not now furnish data whereon to 
found a strictly philosophical hypothesis; but that if the experience of 
the gardener have satisfactoy'ily proved that soap-lather destroys the 
uredo or other mildew fungus,—I hold it to be beyond question or 
doubt, from actual proof, that the remedy exists in, and is solely to he 
