P L A 



OR, BOTANICAL DICTIONARY. 



P L A 



355 



such a length as to hurt the plant materially. The Follicidus 

 carnosus foliorum, is a gall of a particular kind, which is 

 subulate and acute. It is found in Populus nigra and Tilia 

 Europcea, and covers the whole surface of the leaf. It arises 

 in the same way as the former, and by its great number 

 sometimes sickens the plant. Contortions, owe their origin 

 likewise to insects, which produce a swelling and contortion 

 of the leaves ; hence they become contorted, which is the 

 characteristic feature of the disease. It occurs in Cerastium, 

 Veronica, Lotus, Vaccinium. Verruca, or wart, is a small 

 protuberance, which occurs chiefly in fruits, for instance, in 

 apples. Here insects are not the cause, but accidental 

 occurrences. Of the same kind are the moles. They arise 

 from the wounds of the cutis. Both diseases are not hurtful, 

 and, as yet, we know no means to prevent them. Tuber 

 lignosum, is met with on trunks of trees. It seems to be pro- 

 duced partly by insects, partly by changes of weather. It 

 arises from a disturbance in the active vessels of the inner 

 bark, which by the application of stimuli several times con- 

 volve, without forming buds or boughs. They form, instead 

 of this, great knobs, which often, in a bad situation, espe- 

 cially through moisture, exulcerate. It not unfrequently 

 grows very large, without the least injury to the tree. 

 Squamationes, or spongy swellings, are produced like galls. 

 A small insect lays its eggs in the apex of a bud. Thus 

 injured, the branch, which was to be formed from the bud, 

 cannot be properly unfolded, it remains quite short ; all its 

 leaves, therefore, expand themselves from one point, but they 

 are of small size. The whole has somewhat the appearance 

 of a rose. This may be often seen in willows. Such spongy 

 swellings are of bad consequence when in great numbers. 

 The only way to extirpate them, is, to cut them off before 

 they are properly formed. The Bedeguar occurs in roses 

 only, and has the same origin as the former, with this differ- 

 ence, that the insect which gives rise to the bedeguar, depo- 

 sits a number of eggs in one heap, in the middle of the bud. 

 From this a fleshy mass of the size of a fist arises, which is 

 covered all over with hair-like coloured elongations, but 

 never has leaves. Chlorosis, is that affection of plants, when 

 their green colour entirely disappears, and all their parts 

 grow whitish. It arises from diminished stimulus, the plants 

 cannot excrete their oxygen, which therefore is accumulated. 

 There are three causes of the disease : want of light ; insects ; 

 and bad soil. As soon as the plant is deprived of light, it can- 

 not disengage the oxygen, hence it assumes a white colour, 

 which however instantly goes off when the rays of the sun 

 are again admitted. This is the reason why plants, in dark 

 rooms, between great masses of stone, in deep clefts of rocks, 

 beneath the dark shade of shrubs and trees, &c. grow pale, 

 and of a whitish colour. Insects, which bite off the radicles 

 of plants, or even nestle in them, and consume their food, 

 debilitate their vessels, render them insensible of the stimulus 

 of light, and at last chlorotic. This occurs very frequently 

 in Secale cereale. Here no remedies are of any use. Impro- 

 per soil, from which plants do not get a sufficient quantity 

 of proper food, sometimes renders them chlorotic. In such 

 cases plants may recover by change of soil. Icterus, differs 

 from chlorosis, only in its colour, and by its cause, which 

 is cold coming on early in autumn. It is indeed the natural 

 death of the leaves, and can only hurt the plant itself when 

 the cold begins in autumn before the due time. Anasarca, 

 or dropsy, rises in plants from long-continued rain, or too 

 profuse watering. Single parts, in this case, are preterna- 

 turally swelled, and commonly putrefy. Some of the bulbous 

 and tuberous roots, for instance, are often greatly swelled 

 after rain. Fruit becomes watery and tasteless. Seeds do 

 VOL. it. 95. 



not get ripe, or the plant pushes out young shoots unseason- 

 ably from the stem. Most of the succulent plants suffer from 

 too copious a supply of water. Anasarca in plants is gene- 

 rally incurable. Phthiriasis, is that disease of plants where 

 the whole is covered with small insects, which suck out 

 all its sap, suppress the function of transpiration, and of 

 course hinder the farther evolution of its parts. This disease 

 is produced by three different species of insects. By the 

 Aphis, of which each plant has almost a peculiar species. 

 By the Coccus, of which there are various species. That 

 which in our hot-houses is mostly met with, the Coccus hes- 

 peridum, is the most dangerous ; those which are commonly 

 found on the roots of Scelanthus, Polygonum, and others, 

 are less noxious. The disease is, lastly, produced by the 

 Acarus telarius, a small mite, which in hot-houses likewise 

 spins a very delicate web over the leaves of the plants, and 

 thus destroys them. Against the Aphis, careful cleaning, or 

 even brushing with suds, or a decoction of tobacco, or strong 

 fumigation with tobacco, or sulphur in close rooms, may be 

 of service. The same means may be employed against 

 the second species, where it may likewise be very beneficial 

 to place the plant, as soon as the temperature is mild, in the 

 open air, in a shady but airy place. This last destroys the 

 canker, which in hot-houses chiefly attacks the genera Sida, 

 Hibiscus, Dolichos, and Phaseolus. Verminatio, or worms, 

 is not, as in the animal kingdom, produced by worms, but 

 by the larvae of insects. The stem, leaves, and fruits, are 

 attacked by it. The stem of some trees is very often eaten 

 through, and must sometimes entirely decay on this account. 

 The willow, Salix alba ; horse-chesnut, .Ssculus hippocasta- 

 num ; and Typha latifolia, may, in regard to the stem, serve 

 as very common instances. The leaves are often inhabited 

 by the well-known mining-worm, especially the leaves of 

 cherry-trees. Fruits, as plums, apples, pears, hazel-nuts, 

 and the grain of corn, and the like, are inhabited by the 

 larvae of insects, which sometimes destroys them. Except 

 the destruction of the larvae, no remedies will resist these 

 ravaging enemies. Tabes, or the consumption of a plant, is 

 frequently a consequence of the already mentioned diseases, 

 or those which we have still to explain. It may however also 

 originate from sterile or improper soil, unfavourable climate, 

 awkward transplanting, exhaustion of strength from too fre- 

 quent flowering, insects, ulceration, &c. The whole plant 

 gradually begins to decline, and dries up. As soon as this 

 disease really appears, help is rarely possible. Teredo pino- 

 rum, is a kind of tabes, which attacks principally the albur- 

 num and inner bark of Pines. The disease arises from long- 

 continued dry weather, or violent frost of long duration, 

 especially after preceding mild or warm weather, and violent 

 gales of wind. Its signs are, an unusual discolouring of the 

 acerous leaves, which are more or less of a reddish yellow 

 hue. A great number of small drops of resin appear on the 

 boughs, and, lastly, a putrid turpentine-like odour spreads 

 in their neighbourhood ; the bark comes off, and the albur- 

 num presents a blackish-blue appearance. At the same time 

 the well-known beetle appears, with several similar species 

 of insects. The Teredo is an incurable disease, and in large 

 forests nothing more can be done than to permit the removal 

 of the pointed leaves or the moss round the roots of the Pine 

 trees, as the trees are thereby weakened, and so much sooner 

 exposed to this misfortune. -Dcbilitas, s. deliquium. Plants 

 which suffer from debility have all their p'arts, stern, leaves, 

 flowers, &c. hanging down quite relaxed. Debility owes it 

 origin to foul air, want of light, of leaves, or of moisture, 

 too strong light, and other causes, which we must endea- 

 vour to remove, in order effectually to remedy this evil. 

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