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P L A 



THE UNIVERSAL HERBAL; 



PL A 



tree for bringing up the silk-worm, should be avoided, or at 

 least done with moderation. Insects which are noxious to 

 plants, should be accurately known, and their way of propa- 

 gation understood, in order to obviate the bad effects which 

 they produce, and to check their too great increase. Change 

 of place is the only means of preventing the noxious influence 

 of acrid fumes, of great manufactures andiron-works, and the 

 like, as well as of dust. In long-continued drought, careful 

 watering is advisable. The falling off of the leaves in autumn 

 is quite consistent with nature, and of no bad consequence 

 whatever; except, perhaps, when the leaves are dropping off 

 too soon, on account of early night-frosts, and these can affect 

 only delicate foreign plants, of which care should be taken. 

 Hamorrhagia, is of two kinds, spontaneous, or occasioned 

 by wounds. The Birch and Maple, when wounded, emit a 

 great quantity of juice, which, when allowed to flow too 

 copiously, may end in the death of the plant. Spontaneous 

 hsemorrhagy arises from the great irritability of the plant, 

 and the soil is generally the accidental cause. The soil is 

 either what, in common language, is called too rough, that 

 is, it promotes too rapid a separation of the juices, which, on 

 account of their large quantity, cannot be received into the 

 vessels, and therefore must be discharged, and then they 

 acquire in the air a corrosive property, by which the parts 

 are destroyed ; or the soil is too rich in general, rendering 

 the plant full of juices, but unable to retain the moisture, 

 which, therefore, without corroding the posterior parts, they 

 discharge, or deposit only externally their gummy constituents. 

 In most cases, spontaneous hsemorrhagy is incurable. Spon- 

 taneous hsemorrhagy, from superabundance of sap, is either 

 gummous, as in fruit-trees, or of a watery nature, as in the 

 Vine. This last species has been styled lachrymatio. The 

 gummous hsemorrhagy proves rarely fatal, but should not be 

 allowed to make too much progress, and the wound should 

 be healed up by wax. The watery haemorrhagy in the Vine, 

 has no bad consequences whatever; for this plant is the 

 same in winter as all ligneous plants. The radicles of it, 

 which have been formed during the cold season, imbibe a 

 great deal of moisture from the ground, which they convey to 

 the stem. But as the weather is not soon enough favourable 

 for the shooting of it, and as the radicles imbibe more sap 

 than the tender stalks can contain, the superfluous sap exudes 

 from the gems or buds. In warm climates, the Vine does not 

 lachrymate; for there the leaves can unfold themselves in- 

 stantly, and the sap of course is properly digested. This 

 watery discharge of the Vine is not, therefore, to be considered 

 as a natural secretion, peculiar to the plant, but as the effect of 

 cold climates. It, however, does not hurt the plant. Albigo, 

 or mildew, is a whitish mucilaginous coating of the leaves of 

 plants, which often causes their decay. It is produced by 

 small plants, or by insects. The first kind appears on the 

 leaves of Tussilago/ar/ara, Humulus lupulus, Corylus avel- 

 lana, Lamium album, purpureum, and others. It is a small 

 species of fungus, of great minuteness, which covers the 

 leaves : Linneus calls it Mucor Erysiphe. The second kind 

 is a whitish slime, which some species of Aphis deposit on 

 the leaves. As soon as there is the least appearance of mil- 

 dew, all the leaves stained with it should be plucked off and 

 burned. In scarce and delicate plants, the leaves ought to 

 be washed. But where it is produced by aphides, a weak 

 decoction of the dry leaves of tobacco will be found most 

 xerviceable. But if all parts of a plant are attacked, and the 

 plant is hard and of long duration, then the parts must, accord- 

 ing to the nature of the plant, be taken oft. If it is an 

 annual plant, and of great delicacy, it will be best to wash it 

 with a brush dipped in the decoction of tobacco, and after- 



wards to expose it to the open air. Melliyo, or honey-dew, 

 is a sweet and clear juice which, during hot weather, is fre- 

 quently found upon the leaves, rendering them sticky, and, 

 especially when there is a want of rain, causing them to fall 

 off. This sweet matter is likewise secreted by aphides, from 

 peculiar glands at the anus. In tender plants, washing with 

 water, or with the above decoction, is of great benefit; the 

 fumes of tobacco, likewise, kill the insects. Rubigo, or rust, 

 appears on the leaves and stems of many plants. It consists 

 of yellow or brown stains, which, when touched, give out a 

 powder of the same colour, which soils. Microscopical 

 examination has shewn, that the rust-like matter is a small 

 fungus, which is called jEcidium, and the seed of which form 

 this brownish soiling powder. We find them frequently in 

 the leaves and stems of Euphorbia cyparissias, Berberis vulga- 

 ris, Rhamnus catharticus, of some Gramina, of Wheat, Oats, 

 &c. If they are very numerous, especially in the different 

 species of Gramina and Corn, consumption of the whole plant 

 is the consequence. Little can be done against this affection. 

 In grain, some have recommended to moisten the seed, before 

 sown, in salt or lime-water, or to sow grain from countries 

 where this disease does not prevail. Precautions are of no 

 use. Lepra, is frequently met with on the trunks, especially 

 of young trees. If trunks are so entirely covered with algse, 

 that the pores of the cutis are obstructed, we call the dis- 

 temper lepra. Old trees have their trunks full of algse, with- 

 out suffering any injury, provided the smaller branches be 

 free of lliern. But if young trees or shrubs grow in too 

 sterile a soil, in too thin a stratum of fertile soil, in gravelly 

 soil, in improper situations, too moist or too dry, if they are, 

 against their nature, too much exposed to wind, then they 

 sicken, their bark cannot perform, with proper vigour, the 

 functions peculiar to it, as the skin of the tree, and they grow 

 at last, even at their young boughs, all over with fungi of all 

 kinds. Vigorous adjacent plants, which are perfectly sound, 

 will have few or no fungi on their stems. The lepra increases 

 sickness in plants, and they die at last of a consumption, if 

 not cleared of the fungi, if their cutis is not washed, and they 

 are not transplanted to better situations and more proper 

 soils. Gallae, or galls, are produced by small flying insects, 

 the cynips of Linneus. Galls are round, fleshy, variously 

 shaped bodies, which appear on the stem, petioles, peduncles, 

 and the leaves. They are formed in the following manner : 

 The little insect pierces with its sting the substance of the 

 plant, and deposits its eggs in this small aperture. The few 

 air-vessels thus injured get a different direction, and twist 

 round the egg. The irritation which the sting produces 

 occasions, as always in organized bodies, a greater flow o. 

 the sap towards the wounded place ; the sap is deposited in 

 greater quantity than it ought to be, and a fleshy excrescence 

 arises. The little larva which leaves the egg is nourished by 

 the sap, grows up, changes into a pupa, and escapes at last 

 as a perfect insect, which propagates itself again in the same 

 way. It is singular, that each particular fly produces a gall 

 of a peculiar form. This, perhaps, may depend on the pecu- 

 liar structure of the eggs of each species; for we find, that 

 the eggs of different insects, when viewed with the microscope, 

 assume peculiar shapes. On the Oak-tree, we find a variety 

 of galls ; likewise on the Salix, Cistus, Glechoma, Veronica, 

 Hieracium, Salvia, and other plants. The galls of Salvia 

 pomifera, which got its name from that circumstance, are 

 said to be of a pleasant taste, and are considered as an excel- 

 lent dish in the Oriental countries. To remedy this affection, 

 we can do nothing, but cut off the galls as soon as they ap- 

 pear; yet this can be done only in very delicate plants, which 

 we wish to preserve. The disease, however, rarely proceeds 



