fungus gain admission, and at the bottom of the hollows to which they lead, germinate and probably push their minute roots into the cellular texture beyond the bark, where it is supposed they draw their nourishment by intercepting the sap which was intended by nature for the nutriment of the grain. The corn becomes shrivelled in proportion to the number and activity of these fungi, and as the kernel only is abstracted from the grain while the cortical part remains undiminished, the proportion of flour to bran in blighted corn is always reduced in the same degree as corn is made light.
Sir Joseph goes on to observe, that the leaf is probably first infected in the spring or early in the summer, before the corn shoots up into straw, and that the fungus is then of an orange color. After the straw has become yellow, the fungus assumes that of a deep chocolate brown. Each individual is so small that every pore on a straw will produce from twenty to forty fungi, as may be seen in Mr. Bauer's plates, and every one of these will produce at least a hundred seeds. If each of these branches out, therefore, into the number of plants which are represented at the bottom of a pore in one of the plates, the increase must be incalculably great, and a few diseased plants scattered over a field must be sufficient to infect a whole parish. The seeds being very little heavier than air are wafted by every breeze, and are attached by the slightest moisture to the devoted plants.
Such is Sir Joseph's hypothesis concerning the cause of mildew or blight (which he seems to consider as the same thing) in corn. There seems room for suspicion that it is not perfectly correct. Sir Joseph appears to have mistaken, ab principio, an effect for a cause, or at least a proximate cause for a remote one.
On the surface of all diseased and putrid vegetable matter a mucor or mouldiness is formed. In wine vaults, in rotten timber, in
the footstalk of each leaf, and near the base, is attached a small bag, shaped like a pitcher, of the same consistence and colour as the leaf in the early stage of its growth, but changing with age to a reddish purple; it is girt round with a lid, neatly fitted, and moveable on a kind of hinge or strong fibre, which, passing over the handle, connects the vessel with the leaf. By the contraction of this fibre the lid is drawn open whenever the weather is showery, or dews fall, which would appear to be just the contrary of what usually happens in nature, though the contraction probably is occasioned by the hot and dry atmosphere, and the expansion of the fibre does not take place until the moisture has fallen and saturated the pitcher: when this is the case the cover falls down, and it closes so firmly as to prevent any evaporation from taking place. The water being gradually absorbed through the handle into the footstalk gives vigour to the leaf and sustenance to the plant. As soon as the pitchers are exhausted, the lids again open to admit whatever moisture may fall; and when the plant has produced its seed, and the dry season fairly sets in, it withers, with all the covers of the pitchers standing open."
