PHY 



OR, BOTANICAL DICTIONARY. 



PHY 



303 





below the surface of the ground. In the Palmee, however, 

 according to Daubenton's observation, this is very different. 

 For if we cut a stem horizontally through, we find no differ- 

 ence between an old or young tree. In them, the vascular 

 bundles do not dispose themselves in a circular form. They 

 consist of vessels running in a straight line, without regular 

 order, and inclosed by a cellular membrane. Nor do they 

 grow thicker annually, or possess proper bark, but this is 

 formed by the remnants of the leaves. Daubenton is not 

 inclined to assign the name of wood to their substance ; and 

 proposes, if it were to be given to their fibrous substance, 

 the name of lignum fasciculatum, to distinguish it from the 

 common wood, which he calls lignum reticulatum. As the 

 Palmee are destitute of branches, their leaves do not arise 

 from buds, but are in fact only small separated bundles of 

 vessels of the stem, which expand in a leafy form. Hence it 

 is that the under part of the petiolus remains, and forms the 

 bark. If the vascular bundles of a tree or shrub remain in a 

 straight direction, the stem ascends without forming any 

 branches. The new shoots in the Hazel, (Corylus avellana,) 

 Berberis valgaris, and all which the trunk of trees produced 

 when lopped, are a proof of this. As soon, however, as the 

 air-vessels become convoluted, and form a knot, branches 

 are formed. By assistance of art, such straight shoots 

 may be brought to branch, by making a transverse in- 

 cision through the bark. The separated air-vessels heal, 

 the lips of the wound are several times convoluted, and 

 growing larger, are obliged to form more gems, from which 

 branches arise. 



" The growth of ligneous plants admits of five varieties : 

 1. Trees and shrubs, have their stems beset with leaves. On 

 the base of each petiolus a bud or gem is formed, which 

 again becomes a leafy branch, provided with gems formed in 

 the same manner. If the main shoot grows at first in a 

 straight line to a certain height without the buds on its sides 

 being able, on account of the too hasty circulation of the sap, 

 to form themselves into branches, or these, shpuld they really 

 be formed, not be able to grow any more, such a plant then 

 becomes a tree, which has a straight and simple stem, with a 

 branching divided top. But if the stem divides near the root, 

 when the sap circulates more slowly, and each bud can un- 

 fold a branch, then this plant is a shrub. By means of change 

 of soil, place, climate, and by art, trees may be changed into 

 shrubs, and vice versd. 2. Under-shrubs, have very leafy 

 branches, which, however, are very small, and only deposit 

 a very delicate circle of vessels. Hence every bud attached 

 to a petiolus is not then really evolved, as their branches are 

 very few. They are besides, as their branches are so deli- 

 cate, of short duration, and often replace their old decayed 

 branches, by young shoots from the roots. 3. The Pine tribe, 

 have, however, very leafy branches, which on their extreme 

 points only, and on one spot, evolve several buds, of which 

 that in the middle grows in a straight direction, the other 

 unfolding on its sides. Hence the appearance of some Pines 

 like that of a twirling stick, by which, as every year a new 

 one is added, the age of the tree may be found. 4. Shrubby 

 Gramina, have a knotty culm, with attached and dispersed 

 leaves. Each knot sends forth branches; but without a knot 

 no branches appear. 5. Palmse &tL\\\a.frutescentia. These 

 have a simple stem, which has leaves only at its top ; and if 

 this be injured, the stem decays. The last sometimes retain 

 their life by lateral branches, but with the loss of the beauty 

 of their growth and appearance. Besides these varieties of 

 ligneous plants, there are many which make a transition from 

 one to the other. The Palms are incontestably the most 

 beautiful of all ligneous stems, which kind nature has 



VOL. II. 91. 



bestowed on the warm climates exclusively. But after them, 

 the particular growth of some West India trees, which are 

 not of the Palm tribe, deserve notice. To those belong the 

 genera Theophrasta and Spathelia. They have a simple, 

 very high, branchless stem, which in its whole surface is orna- 

 mented with bundles of leaves. How wonderful must be the 

 appearance of a landscape with groups of such trees ! A 

 tree which grows in Africa, on the Senegal, presents the most 

 irregular appearance, and without question is the thickest tree 

 on the globe : it is the Adansonia digitata. Its stem is only 

 ten or twelve feet high, but so thick that its diameter is found 

 to be from 25 to 30 feet. Its circumference, therefore, is 

 from about 75 to 90 feet. Its top is very remarkable ; for 

 numerous and thick branches, of from 30 to 60 feet in length, 

 runout from it in all directions. We ought, therefore, not to 

 be surprised that sometimes the hollow trunk of the Adansonia 

 is the abode of several negro families. Not less Wonderful is 

 the tree called Rhizophora mangle, which bends its branches 

 perpendicularly to the ground, and changes them into stems, 

 so that one single tree covers the muddy rivers under the 

 tropics of Asia, Africa, and America, for more than a mile, 

 with a forest consisting of numberless stems, which at the top 

 have the appearance of a close-clipped bower. But there 

 are varieties of stems, which at first sight scarcely would be 

 counted as such ; and which also, in regard to the structure 

 of their vessels, are different. The whole genus Cactus, with 

 its varieties, is an instance of this kind. The different links 

 which commonly are taken for leaves, are parts of the stem. 

 The leaves themselves are subulate fleshy points, which on 

 their base are covered with small prickles. They fall off, as 

 soon as a bark is properly formed, and their former place is 

 marked by the remaining bundles of prickles. The stem of 

 some species of the genus Euphorbia, Cacalia, and Stapelia, 

 is of the same nature. The links of the stem consist of a 

 double net-work of air and adducent vessels ; the whole is 

 surrounded with a dense cellular texture, or a fleshy substance, 

 and the cutis itself has net-work of lymphatic vessels with 

 apertures. The thorn, is, with regard to its anatomical struc- 

 ture, to be considered as a ligneous stem, and does in no 

 respect differ from it. It arises generally from an incompletely 

 evolved bud, which has begun to form itself, but wanting a 

 proper supply of nourishment, remains only hi form of a very 

 short, sharp, and bare twig. It is like the woody stem of a 

 tree or shrub, formed of the air and adducent vessels, which 

 have grown completely hard. It therefore remains fixed, 

 though the bark be taken off. That it arises from a want of 

 food, is easily proved by the cultivation of thorny plants. 

 Most species of our fruit trees have thorns, but having been 

 supplied in our gardens with extra food, the thorns become 

 boughs, and at last disappear entirely. Only such plants as 

 the Black Thorn, which are almost covered with thorns, do 

 not lose them entirely by that treatment, though the number 

 is always diminished. Nearly the same thing takes place in 

 thorns which are not formed from imperfectly evolved buds, 

 but are other parts of plants, changed in their appearance. 

 Sometimes the petioli of pinnate leaves, when they remain 

 after the leaves have dropped off, become thorns, as in Astra- 

 galus tragacantha, and other species of that genus. On the' 

 petiole they grow larger, sharper, and assume, after the flower 

 and fruit have fallen off, the shape of thorns ; for instance, 

 Hedysarum cornutum: or lastly, the stipulse become sharp, 

 ligneous, remain, and change into thorns; for instance, in the 

 Mimosa. Such changes, which frequently occur, especially 

 in Oriental plants, remain uniform or constant. The prickle, 

 is a prolongation of the cutis, and can therefore be taken off 

 along with it. This consists of reticular, more or less ex- 

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