sons who are accustomed to the management of wall fruit-trees know how slight a screen is sufficient to protect them from its effects. Three or four trees standing together in a hedge-row may so mitigate the severity of frost on the ridges which they screen, that the plants on those ridges, if injured at all, would soon recover their vigor.
Once more—if there are any spots in a field particularly wet, there the corn is sure to suffer most. The reason is obvious: the more succulent a plant is, and the greater the quantity of moisture it has imbibed, the more susceptible must it be of injury from frost; the fuller its vessels are the more liable are they to be ruptured. Farmers, whose fears are always alive, anticipate a mildew from the continuance of a raw and foggy air in the spring or early part of the summer: nor are they often mistaken. In such a continued state of atmosphere, the grasses open their innumerable orifices, and imbibe a prodigious quantity of moisture; if a biting frost immediately succeeds, much mischief may reasonably be apprehended from the rupture of those vessels through which the necessary circulation is to be carried on.
It is said that wheat in the neighbourhood of barberry bushes seldom escapes the mildew: Sir Joseph supposes that the parasitic fungus which often attacks the barberry as well as the wheat, is one and the same species, and that the seed is transferred from the barberry to the corn. The plan which he proposes for preventing the spread of the disease is amusing enough, and reminds one of Dr. Last's celebrated cure for corns, "I pluck 'em up by the roots," quoth the Doctor; thus Sir Joseph Banks recommends the farmer to search diligently in the spring of the year for every infected plant, and to pull it up by the roots. Alas, the age of Hercules is gone!
I began with expressing an apprehension that the disease was irremediable: to ascertain the cause which produces it may in some few cases possibly lead to its prevention. Perhaps a very early luxuriance of the grass of wheat is to be deprecated: where the soil is light and fertile, therefore, and where the situation is sheltered and warm, it may be better to sow wheat at Christmas than at Michaelmas. An instance in which I saw the advantage of this was mentioned before. Perhaps it is unwise to sow wheat on newly broken-up lands: they are so rich and so spongy that an unhealthy luxuriance is produced. They should not be trusted with wheat until they are sufficiently drained, and are become firm: the roots of the young plants in such situations are particularly preyed upon by the wire-worm and other insects. This injures their growth, and produces a sickliness which unfits them for resisting the attacks of fungi.
