Ch. X.] ON THE DISEASES OF WHEAT. 157 



Sinclair, have considered them as separate diseases, brought on at different 

 periods, and occasioned by different causes *. The late Presidents of 

 the Royal Society and the Board of Agriculture are therefore, on this 

 point, at variance. The numerous treatises which have been written by 

 ingenious men upon these disorders, have, indeed, in many instances, either 

 neglected their proper distinction, or confounded them with each other ; or 

 else have applied cause to effect, and have so perplexed the subject that it 

 is far easier to applv the facts which they have stated to every-day practice, 

 than to attempt any abstract definition of their respective theories. 



It may be assumed as a principle, tliat the immediate cause of every dis- 

 temper which attacks the plants of wheat may be ascribed to the state of 

 the season, combined with the circumstances of soil, situation, and seed. 

 It is indeed not easy to class them ; but the great body of farmers look upon 

 rust, mildew, and blight as distinct disorders, arising solely from the influ- 

 ence of the atmosphere. 



Mildew they view as a disease which affects the ear, though, as it is called 

 the spotted distemper, it is apparently more injurious to the straw, and is 

 brought on by causes somewhat similar to those which occasion blight, 

 though at a more advanced period of the season. It usually first attacks the 

 leaf, and then the straw, just at the time the corn is blooming ; and when it 

 comes on immediatelv after the first appearance of the ear, the straw will 

 also be affected ; but if the grain be fully formed, then it is but slightly dis- 

 coloured. It has been supposed to arise either from a dewy kind of reddish 

 gum, which attaches itself to the ear ; or from a parasitic plant, or fungous 

 excrescence, which attacks the wheat under peculiar circumstances of air, 

 warmth, and moisture, and to be cs])ecially occasioned by damp, hazy, 

 easterly winds. The following quotation would indicate it to be white ; — 



' Shield the young harvest from devouring bli)^ht. 

 The smut's dark poison, and the mildew white ;' 



but it generally appears first of a dingy red, afterwards succeeded by dark- 

 brown spots, which appear on the stalks from the first or second husk up- 

 wards, rough to the touch, increasing in size, and at last appearing livid, 

 or approaching to black. It hardly ever appears until the period of ripen- 

 ing, but when it has fairly struck a crop, it then effectually prevents both 

 corn and straw from making any further progress, the whole plant a])pa- 

 rently going every day backward, till existence in a manner ceases. The 

 damage thus occasioned depends, liowever, in a great measure upon the 

 time at which the attack takes place, for if early in the season, the crop will 

 be hardly worth reaping; but if the grain be well advanced, the loss is 

 then considerably diminished. 



Rust, like mildew, also seizes on the leaves and straw ; a kind of dust 

 gathers on them, which increases with the disease, and withholds the cur- 

 rent of the sap until the plant is, in a great measure, exhausted: hence 

 the grain is imperfectly filled, and the crop, of course, generally de- 

 teriorated. It is thus described in a small volume lately published by a 

 person of great practical experience, whose work contains much interesting 

 information on the subject of which it treats — 



" Rust first appears on the leaves of strong growing plants of wheat 

 early in May, but is not seen to fix itself injuriously on tlie culms till about 



* See A Short Account of the Cause of the Disease in Corn, called by Farmers the 

 Blight, the Mildew, and the Rust, by Sir Joseph Banks, Bart.; and Result of an In- 

 quiry into the Nature and Causes of the Blight, the Rust, and the Mildew, by Sir John 

 Sinclair, Bart., M.P. 



