192 SCIENCE OF GARDENING. PART II. 



with all decortications that penetrate deeper than the epidermis, particularly if the wound is not protected 

 from the action of the air : if the decortication reaches to the wood, then new bark issues from between the 

 bark and wood, and spreads till it covers the wound. But the result is not the same when the wound is 

 covered from the air. In the season of the flowing of the sap Du Hamel detached a ring of bark, of three 

 or four inches in breadth, from the trunks of several young elm-trees, taking care to defend the decorti- 

 cated 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 the 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 between 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 completely 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. 



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

 dental injuries, either directly to the flower or fruit, by which they are rubbed off or devoured by insects ; 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 themselves ; and one 

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



872. 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 ripened pre- 

 maturely 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 scorching the. roots in an overhot tan- 

 bed at any season. 



SECT. II. Diseases. 



873. 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 following : 

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

 tion, contortion, consumption. 



874. Blight. Much has been written on the nature of blight ; and in proportion as 

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

 increased. 



875. 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 believed 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 gardening ; 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 



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

 leaves which are thos 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 sub- 

 sequent 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 at- 

 tempting 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 



877. 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 ripening 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. 

 (Hole'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 for- 

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

 produced a fair crop. 



878. 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 

 cf 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 minute inspection these patches were found to 



