Several Accidents kill the Plants, or injure their Health, and then the Grains are not filled; as Lightning, the Effects whereof may be observed by the blackish Spots and Patches in Fields of Wheat, especially in such Years as have more of it than usual. Against this there is no Defence.
The other Causes of the Blight, which are most general, and do the most Damage, may, in some measure, be prevented.
One Cause is the lodging or falling of Corn; for then the Stalks are broken near the Ground, whereby many of the Vessels are so pressed, that the Juices cannot pass them; and then the free Circulation is hindered; the Chyle cannot mount in sufficient Quantity to be purified, and turned into Sap; the Defect whereof makes the Plants become languid, and only just able to live; they have Strength enough to linger on to the time of their Period, as in very old Age, but not to bring their Fruit, which is the Grain, to its natural Bulk, nor to fill it with Flour: and the sooner the Stalks fall, the less and thinner the Grain will be.
Hence it often happens, that when Tillage, Dung, and good Land have brought a Crop of Wheat, that in the Months of April and May promise to yield the Owner Five or Six Quarters on an Acre, then in June it falls down, and scarce affords Five or Six Bushels; and that perhaps is so thin and lank, that the Expence of reaping and threshing it may overbalance its Value.
That the falling down of Wheat does cause the Ruin of the Crop, is well known; but what causes it to fall, is not so plain.
And, without knowing the true Causes, ’tis not likely that a Remedy should be found against the Disease.
I take this Weakness of the Stalks, which occasions their falling, to proceed from want of Nourishment, want of Air, want of the Sun’s Rays, or of all Three.
One Argument, that it lodges for want of Nourishment, is, that a rich Acre has maintain’d a Crop of Five Quarters standing, when another poorer Acre was not able to support a Crop from falling, which was but large enough to have brought Three Quarters, if it had stood: and this in the same Year, and on the same Situation. And ’tis very plain, that if one Acre was twice as rich as the other, it must be able to nourish Five Quarters better than the other could nourish Three Quarters.
Air is necessary to the Life and Health of all Plants, tho’ in very different Degrees: Aquatics, which live under Water, are content with as little Air, as their Companions the Fishes.
But Wheat, being a terrestrial Plant, (tho’ in Winter it will live many Days under Water, whilst the slow Motion of its Sap gives it little or no Increase), requires a free open Air, and does not succeed so well in low sheltery Places, as upon higher and opener Situations; where the Air has a greater Motion, and can more easily carry off the Recrements from the Leaves, after it has shaken off the Dews and Rains, which would otherwise suffocate the Plants; and therefore the Leaves are made so susceptible of Motion from the Air, which frees them from the Dews, that would stop in the Recrements at the Vesiculæ of the Leaves, but shaken down will nourish the Plants at the Roots: The want of this Motion weakening the Wheat, ’tis (as Animals in the like sickly Case are) the more unable to stand, and the more liable to be press’d down by the Weight of Rain-water, and more unable to rise up again when down: All which Evils are remov’d by the free Motion of the Air, which shakes off both Dews and Rains, and thus contributes to prevent the falling (or lodging) of Wheat.