128 



HISTORY OF THE VEGETABLE KINGDOM. 



the seat of irritability, and if it is touched witli 

 any sliaip pointed instrument, or if an insect 

 alights upon it,tlie segments 66, 

 immediately collapse, and ad- 

 here so closely that the in- 

 sect is generally squeezed to 

 death in its gi'asp, or at the 

 least, detained a prisoner. A 

 similar susceptibility to the 

 action of accidental stimuli, 

 lias been observed in the leaves 

 of the several British species 

 of drosera or sun devr. But 

 sometimes the irritability re- 

 sides in the flower, and has its 

 seat either in the stamens or style. The foi-mer 

 case we have already alluded to in the blossoms of 

 the common barberry, the stamens of which, 

 when undisturbed, lie reclined upon the petals 

 which shelter the anthers under their concave 

 tips. But no sooner is the inner side of the 

 filament touched either accidentally or inten- 

 tionally, with any sharp pointed substance, than 

 the stamen immediately bends itself inwards, 

 till its anther strikes against the stigma. This 

 fact had been long familiar to botanists; but it 

 remained to be ascertained whether the suscep- 

 tibility in question was confined to the inner 

 side of the filament mei'cly, or whether it per- 

 vaded the whole stamen. With this object in 

 view. Sir J. E. Smith havingprocured some flowers 

 fully blown, on the 25th of May, examined them 

 with great care ; and after applying the point of 

 a quill or fine bristle, with all possible delicacy, 

 to every part of the surface of the stamen, he 

 found that it no where exhibited any indications 

 of susceptibility, except on the inner side of the 

 filament, and towards the base. It had been 

 thought that the stamens possessed this property 

 only at the time of shedding the pollen; but Sir 

 J. E. Smith found that they possess it at all ages, 

 and even when the petal with its annexed filament 

 has fallen to the ground, they gradually re- 

 cover their original situation, and are capable of 

 being again stimulated as before. The stamens 

 of cactus tuna, a soi-t of Indian fig, are said to 

 be endowed with a similar irritability. If a quill 

 or feather is drawn across its long and slender 

 filaments which surround the germen in great 

 numbers, they will immediately begin to bend 

 to the one side, and wiU in a short time sink 

 down to the base of the flower. The case in 

 which the seat of irritability is confined to the 

 stylo is exemplified in stt/Udium fflandulosum, 

 a native of New Holland. The style of this 

 flower, which is about an inch in length, is bent 

 backward a little above the base, in the manner 

 of the piece of iron that is fixed to the end of a 

 shepherd's crook, or to the end of the pole of a 

 chaise, so that the style forms a sort of hoolc 

 with the flower-stalk, the stigma being reflected 



so as in many cases to touch it. But if the 

 stigma is itself touched with the point of the 

 finger or other suitable instrument, tlie style is 

 immediately put into motion, and flies back till 

 it bends itself as much in a contrary direction, 

 and on the other side of the flower as it did in 

 its first direction. 



CHAP. XX. 



DISEASES OF VEGETABLES. 



Veoetablbs being organized structures, are 

 liable to disease as well as animals. The min- 

 uteness and delicacy of their internal cells and 

 tubes render them frequently liable to disorgan- 

 ization; and their soft and succulent exteriors 

 are continually exposed to abrasions and injuries 

 from the contact of other bodies. Besides these, 

 the influence of the atmosphere, as regards its 

 moisture and dryness, or electric condition, ma- 

 terially affects the health and vigour of plants. 

 Vegetables, like animals, are also liable to the 

 attacks of parasites ; and thus fungi or minute 

 plants, and insects and animalcules, have a very 

 prejudicial effect upon many plants. The diseases 

 of vegetables have been classed under the fol- 

 lowing heads : blight, smut, mildew, honeydew, 

 dropsy, flux of juices, gangrene, etiolation, suffo- 

 cation, contoi-tion, consumption. 



Blight. This is one of the most common 

 diseases which affect vegetables, and yet one on 

 the nature of which the greatest differences of 

 opinion have prevailed. The disease seems to 

 have been observed by, and to have been familiar 

 to the ancient Greeks. They regarded it as a 

 scourge from heaven, or from their enraged 

 deities; and therefore did not trouble themselves 

 in the investigation of its nature or cause. It 

 was familiar to the Romans also, under the 

 name of ruhigo, or rust; and this people regarded 

 it in the same light as the Greeks, believing it, 

 however, to be under the special influence of a 

 particular deity named Ruhigus, whom they 

 solemnly invoked in order to keep this calamity 

 from their trees and corn fields. In modern 

 times it is not less well known ; yet still its true 

 nature remains matter of speculation. The 

 fact is, that there may perhaps be several varie- 

 ties, and the disease all arising from different 

 causes, 



Dr Keith has endeavoured to point out at 

 least three species, 1st, Blight ai'isingfrom cold 

 and frosty winds : 2d, from a peculiar vapour, 

 perhaps originating in certain electric conditions 

 of the atmosphere : and, ,3d, from the presence of 

 a minute parasitical fungus. 



The first kind of blight is often occasioned by 

 the cold and easterly winds of spring, which nip 



