AND THE STRUCTURE OF PLANTS. 



87 



natans)jihe germ must necessarily be supported in the first instance by means 

 of the cotyledon. 



It is the corcle which is the true pvnctum saliens of vegetable life, and to 

 this the cotyledon is subservient. The corcle consists of two parts, an 

 ascending and a descending ; the former called its plumule, which gives birth 

 to the trunk and branches; the latter nairsed its rostel, which gives birth to 

 the root and radicles. The position of the corcle in the seed is always in 

 the vicinity of the hilum or eye, which is a cicatrix or umbilicus remaining 

 after the separation of the funis or umbilical cord from the pericarp, to which 

 the seed has hereby been attached. The first radicle or germinating branch 

 of the rostel uniformly elongates, and pushes into the earth, before the plu- 

 mule evinces any change. Like the cotyledon, the radicles consist chiefly of 

 lymphatics and air-vessels, which serve to separate the water from the soil, 

 in order that the oxygen may be separated from the water. 



Hence originates the root, unquestionably the most important part of the 

 plant, and which in some sense may be regarded as the plant itself: for if 

 every other part of the plant be destroyed, and the root remain uninjured, 

 this organ will regerminate and the whole plant be renewed ; but if the root 

 perish, the plant becomes lost irrecoverably. Yet there are various pheno- 

 mena in vegetable life that manifest a smaller diff"erence in the nature of the 

 root and the trunk, than we should at first be induced to suppose ; for Wil- 

 loughby observed, more than a century and a half ago,* that in several spe- 

 cies, and especially those of the prunus and salix, cherry and willow tribes, 

 if the stem branches be bent down to the earth, plunged into it, and continued 

 in this situation for a few months, these branches will throw forth radicles ; 

 and if, after this, the original root be dug up, and suffered to ascend into the 

 air, so that the whole plant become completely inverted, the original root will 

 throw forth stem-branches and bear the wild fruit peculiar to its tribe. The 

 rhizophora Mangle^ or mangrove-tree, grows naturally in this manner; for 

 its stem-branches, having reached a certain perpendicular height, bend down- 

 wards of their own accord, and throw forth root-branches into the soil, from 

 which new trunks arise, so that it is not uncommon, in some parts of Asia 

 and Africa, to meet w^th a single tree of this species covering the oozy waters 

 in which it grows with a forest of half a mile in length. The ficus Indica, 

 or banyan, grows in the same manner, and often with enormous trunks, 

 equally derived from a primary root. The largest tree of this kind known 

 to Europeans, is on an island in the river Nerbedda in the Guzzerat, distin- 

 guished in honour of a Bramin, of high reputation, by the name of Cubbeer 

 Bur. High floods have destroyed many of its incurved stems, yet its princi- 

 pal stems measure two thousand feet in circumference, the number of its 

 larger trunks, each exceeding the bulk of our noblest oaks, amount to three 

 hundred and fifty, while that of its smaller are more than three thousand ; so 

 that seven thousand persons may find ample room to repose under its enor- 

 mous shade, and may at the same time be richly supplied from the vast abun- 

 dance of fruit which it yields in its season. 



The solid parts of the trunk of the plant consist of cortex, cuticle, or 

 outer bark ; liber, cutis, or inner bark ; alburnum, or soft wood ; lignum, or 

 hard wood ;t and medulla, or pith. Linnaeus gave the name of medulla to 

 the pith of plants, upon a supposition that it had a near resemblance to the 

 medulla spinalis of quadrupeds. A closer investigation, however, has since 

 proved that this resemblance is very faint, and that the pith or medulla of 



* Phil. Trans, year 1669, iv. p. 963—1670, v. p. 1165. 1168. 1199,-1671, vi. p. 2119. 



t There is a curious paper of Count Rumford's, mentioned among the labours of the French Imperial 

 Institute for 1812, upon the chemical proi)erties of the different parts entering into the composition of the 

 trunk of trees ; for an account of which see alsoTliomson's Annals of Philos. vol. i. p. 386. By a variety 

 of experiments Count Rurnford was led to this singular conclusion, that the specific gravity of the solid 

 matter which constitutes the timber of wood is almo.st the same in all trees. By the same means he deter- 

 mined that the woody part of oak in full vegetation is only four-tenths of the whole. Air constitutes one- 

 fourth of it, and the rest consists in sap. Light woods have still a much less quantity of solid matter: 

 but the season of the year and the age of the tree occasion considerable variations. Ordinary dry wood 

 contains about one-fourth of its weight of water. Even the oldest wood, though in the state of timber for 

 ages, never contains less than one-sixth of its weight of water. All absolutely dry woods give from 42 to 

 43 per cent, of charcoal ; whence he concludes, that the ligneous matter is identic in all wcxkIs, 



