260 SCIENCE OF AGRICULTURE. PXrt II. 



which, as they float In the air, enter the pores of the epidermis of the leaf, particularly if the plant 

 is sickly ; or they exist in the manure or soil, and enter by the pores of the root. {Si?- J. Banks on 

 Blisht, 1805.) This fungus has been figured by Sowerby, and by F.Bauer, and Grew. It is known 

 among' fanners by the name of red rust, and as it affects the stalks and leaves only it does not materially 

 which the crop. But there is another species of fungus known to the farmer by the name of red gum, 

 injure attacks the ear only, and is extremely prejudicial. In the aggregate it consists of groups of minute 

 globules interspersed with transparent fibres. The globules are filled with a fine powder, which explodes 

 when they are put into water. It is very generally accompanied with a maggot of a yellow colour, that 

 preys also upon the grain, and increases the amount of injury. The only means of preventing or lessening 

 the effect of any of the different varieties of bliglit mentioned is proper culture. Palliatives are to be 

 found in topical applications, such as flower of sulphur, and where the disease proceetls from, or consists of, 

 innumerable minute insects, it may occasionally be removed. Grisenthwaite conjectures that in many 

 cases in which the blight and mildew attack corn-crops, it may be for want of the peculiar food re- 

 quisite for perfecting the grain ; it being known that the fruit or seeds of many plants contain primitive 

 principles not found in the rest of the plant. Thus the grain of wheat contains gluten and phosphate of 

 lime and where these are wanting in the soil, that is, in the manured earths in which the plant grows, it 

 will be unable to perfect its fruit, which of consequence becomes more liable to disease. {New Theory of 

 Agr. &c.) 



1658. Smut is a disease incidental to cultivated corn, by which the farina of the grain, 

 together with its proper integuments and even part of the husk, is converted into a black 

 soot-like powder. If the injured ear is struck with the finger, the powder will be 

 dispersed like a cloud of black smoke ; and if a portion of the powder is wetted by a 

 drop of water and put under the microscope, it will be found to consist of millions of 

 minute and transparent globules, which seem to be composed of a clear and glary fluid 

 encompassed by a thin and skinny membrane. This disease does not affect the whole 

 body of the crop, but the smutted ears are sometimes very numerously dispersed through- 

 out it. Some have attributed it to the soil in which the grain is sown, and others have 

 attributed it to the seed itself, alleging that smutted seed will produce a smutted crop. 

 But in all this there seems to be a great deal of doubt. Willdenow regards it as origi- 

 nating in a small fungus, which multiplies and extends till it occupies the whole ear. 

 (Princip. of Hot. p. 356.) But F. Bauer of Kew, seems to have ascertained it to be 

 merely a morbid swelling of the ear, and not at all connected with the growth of a fun- 

 gus. (Smithes Introd. p. 348.) It is said to be prevented by steeping the grain before 

 sowing in a weak solution of arsenic. But besides the disease called smut there is also 

 a disease analogous to it, or a different stage of the same disease , known to the farmer 

 by the name of bags or smut-balls, in which the nucleus of the seed only is converted 

 into a black powder, whilst the ovary, as well as the husk, remains sound. The ear is 

 not much altered in its external appearance, and the diseased grain contained in it will 

 even bear the operation of threshing, and consequently mingle with the bulk. But it is 

 always readily detected by the experienced buyer, and fatal to the character of the sample. 

 It is said to be prevented as in the case of smut. 



1659. Mildew is a thin and whitish coating with which the leaves of vegetables are 

 sometimes covered , occasioning their decay and death, and injuring the health of the 

 plant. It is frequently found on the leaves of tussilago farfara, humulus lupulus, cory- 

 lus avellana, and the white and yellow dead-nettle. It is found also on wheat in the 

 shape of a glutinous exudation, particularly when the days are hot and the nights with- 

 out dew. Willdenow says it is occasioned by the growth of a fungus of great minute- 

 ness, the mucor erisyphe of Linnaeus ; or by a sort of whitish slime which some species of 

 aphides deposit upon the leaves. J. Robertson (Hort. Trans, v. 178.) considers it as a 

 minute fungus of which different species attack different plants. Sulphur he has found 

 the only specific cure. In cultivated crops mildew is said to be prevented by manuring 

 with soot. 



1660. Honey-dew is a sweet and clammy substance which coagulates on the surface of 

 the leaves during hot weather, particularly on the leaves of the oak-tree and beech, and 

 is regarded by Curtis, as being merely the dung of some species of aphides. This seems 

 to be the opinion of Willdenow also, and it is no doubt possible that it may be the case 

 in some instances or species of the disease. But Sir J. E. Smith contends that it is not 

 always so, or that there are more species of honey-dew than one, regarding it particularly 

 as being an exudation, at least in the case of the beech, whose leaves are, in consequence 

 of an unfavorable wind, apt to become covered with a sweet sort of glutinous coating, 

 similar in flavor to the fluid obtained from the trunk. 



1661. It is certain, however, that saccharine exudaliom are found on the leaves of many plants, though 

 not always distinguished by the name of honey-dew ; which should not perhaps be applied except when 

 the exudation occasions disease. But if it is to be applied to all saccharine exudations whatever, then we 

 must include under the appellation Of honey-dew, tne saccharine exudations observed on the orange-tree 

 by De la Hire, together with that of the lime-tree which is more glutinous, and of the poplar which is 

 more resinous ; as also that of the cistus creticus, and of the manna which exudes from the ash-tree of 

 Italy and larch of France. It is also possible that the exudation or excrement constituting honey-dew 

 may occasionally occur without producing disease ; for if it should happen to be washed off soon after by 

 rains or heavy dews, then the leaves will not suffer. Washing is therefore the palliative : judicious cut. 

 ture the preventive. 



1 662. Dropsy. Plants are also liable to a disease which affects them in a manner similar 

 to that of the dropsy in animals, arising from long continued rain or too abundant wateriog. 



