Book I. DISEASES OF VEGETABLES. 259 



taking care to defend the decorticated part from the action of the air, by surrounding it with a tube 

 of glass cemented above and below to the trunk. After a few days the tubes became cloudy within, 

 particularly when it was hot ; but when the air became cool, the cloud condensed and fell In drops to tlje 

 bottom. At last there began to appear, as if exuding from between the bark and wood of the upper part 

 of the wound, a sort of rough scurfy substance ; and on the surface of the wood, as if exuding from be- 

 tween the longitudinal fibres of the alburnum, a number of gelatinous drops. They were not connected 

 with the scurfy substance at the top, but seemed to arise from small slips of the liber that had not been com- 

 pletely detached. Their first appearance was that of small reddish spots changing by degrees into white, 

 and finally into a sort of grey, and extending in size till they at last united and formed a cicatrice, which 

 was a new bark. 



IftjO. Abortion or failure in the produce of flowers, fruits, or of perfect seeds, is generally the effect of 

 accidental injuries, either directly to the flower or fruit, by which they are rubbed off or devoured by in- 

 sects ; or to the leaves by insects ; or to the roots by exposure to the air or cutting off so much of them as 

 essentially to lessen their power of drawing up nourishment. Other causes will readily suggest them- 

 selves ; and one of the commonest, as to seeds and fruits, is want of sufficient impregnation. 



1651. Premature inflorescence or fruiting is sometimes brought on by insects, but more generally by 

 checks produced by cold or injuries from excessive heat, or long continued drought. Fruit is often ri])ened 

 prematurely by the puncture of insects ; and a pine-apple plant of almost any age may be thrown into 

 fruit by an hour or two's exposure to a frosty atmosphere in winter, or by scordiing the roots in an over- 

 hot tan-bed at any season. 



Sect. II. Diseases. 



1652. Diseases are corrupt affections of the vegetable body, arising from a vitiated 

 state of its juices, and tending to injure the habitual health either of the whole or part of 

 the plant. The diseases that occur the most frequently among vegetables are the follow- 

 ing : Blight, smut, mildew, honey-dew, dropsy, flux of juices, gangrene, etiolation, 

 suffocation, contortion, consumption. 



1653. Blight. Much has f^een written on the nature of blight ; and in proportion as 

 words have been multiplied on the subject, the difficulties attending its elucidation have 

 increased. 



1654. The blight, or blast, was well known to the ancient Greeks, who were however totally ignorant 

 of its cause, regarding it merely as a blast from heaven, indicating the wrath of their offended deities, and 

 utterly incapable of prevention or cure. It was known also to the Romans under the denomination 

 of rubigo, who regarded it in the same light as the Greeks, and even beheved it to be under the direction 

 of a particular deity, Rubigus, whom they solemnly invoked that blight might be kept from corn and 

 trees. It is still well known from its effects to every one having the least knowledge of husbandry or gar- 

 dening ; but it has been very differently accounted for. And, perhaps, there is no one cause that will 

 account for all the different cases of blight, or disease going by the name of blight ; though they have been 

 supposed to have all the same origin. If we take the term in its most general acceptation I think it will 

 include at least three distinct species blight originating in cold and frosty winds, blight originating in a 

 sort of sultry and pestilential vapor, and blight <iginating in the immoderate propagation of a sort of small 

 and parasitical fungus. 



1655. Blight, originating in cold and frosty winds, is often occasioned by the cold and easterly winds 

 of spring, which nip and destroy the tender shoots of the plant, by stopping the current of the juices. 

 The leaves which are thus deprived of their due nourishment wither and fall, and the juices that are now 

 stopped in their passage swell and burst the vessels, and become the food of innumerable little insects 

 that soon after make their appearance. Hence they are often mistaken for the cause of the disease itself; 

 the farmer supposing they are wafted to him on the east wind, while they are only generated in the extra- 

 vasated juices, as forming a proper nidus for their eggs. Their multiplication will no doubt contribute to 

 the spreading of the disorder, as they always breed fast where they find plenty of food. But a similar 

 disease is often occasioned by the early frost of spring. If the weather is prematurely mild, the blossom 

 is prematurely protruded, which, though it is viewed by the unexperienced with delight, yet it is viewed 

 by the judicious with fear. For it very often happens that this premature blossom is totally destroyed by 

 subsequent frosts, as well as both the leaves and shoots, which consequently wither and fall, and injure if 

 they do not actually kill the plant. This evil is also often augmented by the unskilful gardener, even in 

 attempting to prevent it; that is, by matting up his trees too closely, or by keeping them covered in the 

 course of the day, and thus rendering the shoots so tender that they can scarcely fail to be destroyed by the 

 next frost 



1656. Blight, originating in sultry and pestilential vapor, generally happens in the summer when the 

 grain has attained to its full growth, and when there are no cold winds or frosts to occasion it. Such was 

 the blight that used to damage the vineyards of ancient Italy, and which is yet found to damage our hop- 

 plantations and wheat-crops. The Romans had observed that it generally happened after short but heavy 

 showers occurring about noon, and followed by clear sunshine, about the season of the riiiening of the 

 grapes, and that the middle of the vineyard suffered the most This corresponds pretty nearly to what 

 IS in this country called the fire-blast among hops, which has been observed to take place, most commonly 

 about the end of July, when there has been rain with a hot gleam of sunshine immediately after ; the 

 middle of the hop-ground is also the most affected whether the blight is general or partial, and is 

 almost always the point in which it originates. In a particular case that was minutely observed, the 

 damage happened a little before noon, and the blight ran in a line forming a right angle with the sun- 

 beams at that time of the day. There was but little wind, which was however in the line of the blight 

 {Hale's Body of Husbandry.) Wheat is also affected with a similar sort of blight, and about the same 

 season of the year, which totally destroys the crop. In the summer of 1809, a field of wheat, on rather a 

 light and sandy soil, came up with every appearance of health, and also into ear with a fair prospect of 

 ripening well. About the beginning of July it was considered as exceeding any thing expected from such 

 a soil. A week afterwards a portion of the crop, on the east side of the field, to the extent of several acres^ 

 was totally destroyed ; being shrunk and shrivelled up to less than one half the size of what it had formerly 

 been, and so withered and blasted as not to appear to belong to the same field. The rest of the field pro- 

 duced a fair crop. 



1657. Blight, originating in fungi, attacks the leaves or stem both of herbaceous and woody plants, 

 such as euphorbia cyparissias, berberis vulgaris and rhamnus catharticus, but more generally grasses ; 

 and particularly our most useful grains, wheat, barley, and oats. It generally assumes the appearance 

 of a rusty-looking powder that soils the finger when touched. In March 1807, some blades of wheat were 

 examined by Keith that were attacked with this species of blight ; the appearance was that of a number 

 of rusty-looking spots or patches dispersed over the surface of the leaf, exactly like that of the seeds of 

 dorsiferous ferns bursting their indusium. Upon more nunute inspection these patches were found to con- 

 sist of thousands of small globules collected into groups beneath the epidermis, which they raised up in a 

 sort of blister and at last burst Some of the globules seemed as if imbedded even in the longitudinal 

 vessels of the blade. They were of a yellowish or rusty brown, and somewhat transparent But these 

 group* of globules have been ascertained by Sir J. Banks to be patches of a minute fungus, the seeds of 



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