204 
THE PRINCIPLES OF BOTANY. 
broken-up districts, including newly broken-up pastures. At 
home there is a great liability to the growth of this fungus ; 
and if we want better specimens than usual, we cannot do 
better than seek them in the old dung-heap, where growing 
wheat is sure to be quite black in the straw from this pest, 
which seems to show that a plethora of nutritive or manurial 
matter is the cause of the affection. Salt as a dressing is 
said to be a remedy ; and a former pupil of ours (Mr. Robert 
Holland) has written to us for specimens from that country, 
affirming that it is with them in Cheshire a great rarity, pro- 
bably from the quantity of salt which is there employed as 
manure. 
But whatever the cause of this blight, or whatever its cure, 
it will be found a matter of great importance to every farmer 
and stock-breeder to become well acquainted with it, as how- 
ever abundant the ears or straw, there will assuredly be a 
falling off in the yield of the corn, as well as a depreciation 
in its quality, where the crop is much affected by it, and the 
straw is thereby rendered next to useless except for litter. 
Besides these, almost every plant has its peculiar forms 
of mould and mildew ; thus the mildew of the turnips, both 
the common and Swedish varieties, are well known. The 
hop mildew, again, is a presage of blighted hopes for this 
valuable crop. Potato leaves are also affected with mildew, 
so again are cucumbers and melons, and, indeed, few crops 
but may suffer at some period from the effects of mildew, and 
the forms are so numerous, probably more than one affecting 
some of our species, that it would be endless work to attempt 
even a slight description of them. Suffice it to say that, in 
their curious and delicate forms, the microscopist may find 
matter for something more than amusement, or even admira- 
tion, as their history is very obscure, though, at the same 
time, whether, as some assert, they are the cause of the 
injury to the crop of which their presence is a sure indi- 
cation, or whether they are the result of some previous con- 
stitutional mischief, occasioned by alternation of drought 
and moisture, their more frequent precursors. One thing is 
quite certain, that they result in crops poor both in quality 
and yield. 
It is an interesting fact that the ravages of this tribe of 
plants are at once arrested by the application of flowers of sul- 
phur ; by dusting our greenhouse plants, which suffer enor- 
mously from this cause, we at once arrest the further 
development of mildew ; so both for the hop and vine mildew 
this material is now largely employed. 
How, then, does this act? It may be said to be as great 
