238 
ON THE MILDEW OF PLANTS 
Query 1. Which quality of the soap is it that is thus effectual ? 
and— 
“ Query 2. Would a solution of soda in pure water answer the same 
purpose of the gardener ? ” 
I have bent my attention to this important subject; and only regret 
that to the present time, and ever since the inquiry was made, I have 
had no satisfactory means at hand to afford a fully practical demonstra¬ 
tion of the efficacy of the chemical agents which are particularly men¬ 
tioned. Last year, a very fine bed of the damask rose was so completely 
infested with the fungus, that the leaves curled up, thickened, assumed 
an appearance as if they had been coated with starch, and in all 
respects were totally changed. Had I at this time such an opportunity 
afforded me, I could ere now have arrived at something like a definite 
conclusion. I however destroyed my bed, transplanted my bushes in 
October, and find that scarcely one in ten has survived. The only 
specimens of mildew which I have met with during the late spring 
have been seen on the terminations of two or three laterals upon my 
espalier apple-trees; and these, I have reason to think, were produced 
by the sudden and powerful heat which set in about the first week of 
the present month. On these affected shoots, I have performed several 
experiments, and shall, in a few words, describe the agents I have 
made use of. Before I do this, however, I must observe, that although 
I have not as yet assured myself of a certain curative remedy, I have 
discovered an active agent, which, while it confirms one of Mr. Main’s 
assertions, leads to a reply to the second query. If, for want of data, 
I cannot practically answer the questions which apply to the curative 
agency of soap, I am enabled to present to the reader who may take 
interest in the proposed subject, certain facts upon which he may rely, 
and on them found a series of experiments which may lead to satisfac¬ 
tory results. 
The chemical composition of soap requires our first notice. 
Common soap is composed of soda and fatty substances, as those of 
tallow, grease, oil, and the like : it varies in colour, consistence, and 
odour, according to the nature and condition of the materials employed. 
I do not mean to speak of the manufactory of soap ; that would involve 
an inquiry irrelevant to the subject; but simply to furnish a general 
idea of the ingredients of which soap is composed. The soda or mineral 
alkali made use of by the soap-boiler, is not however that article which 
is sold by the druggist; i t is a liquid in a caustic state, that is to say, 
it is soda deprived of the carbonic acid (which renders it mild) by the 
agency of a certain quantity of quick-lime. Let any curious reader 
take half an ounce of common crystals of soda : on applying his tongue 
