576 



BOTANY. 



ports, but without extracting from them any aliment 

 whatever. 



The foregoing' observations are intended to identify 

 what are really roots from other parts with which 

 they are sometimes confounded. Under-ground stems 

 are often called roots ; such as those of couch-grass, 

 the potato, and other plants which increase them- 

 selves by under-ground runners. 



The structure of roots is very similar, whether 

 succulent or woody. They all have a central mem- 

 ber, formed of longitudinal fibres bedded in cellular 

 and vascular matter, but without any pith. This 

 central body is increased by annual additions to its 

 exterior, in the same manner as the woody axis of a 

 tree is increased. It is also covered with various 

 layers of cuticle or bark ; but which are always 

 thinner, softer, and more spongy than that which is 

 exposed to the air. The roots of some trees, as the 

 elm and whitQ poplar for instance, appear to have 

 the same structure (except in being pithless) as the 

 steins, and moreover are also furnished with buds, 

 which shoot and form suckers all round, and at con- 

 siderable distances from the trunk. 



Roots of trees are more durable than their heads ; 

 and this, perhaps, because they are less exposed to 

 the vicissitudes of weather. Although they gene- 

 rally die soon after the stem is cut over, yet there 

 are many exceptions, as in the case of the two kinds 

 just mentioned ; and there are some remarkable cir- 

 cumstances on recofd relative to the longevity of 

 roots. It is well authenticated that the roots of a 

 mulberry tree when grubbed up, were found fresh 

 and sound, though the tree had been felled forty 

 years before ! And from what has been lately ob- 

 served by an eminent French botanist, the roots of 

 the silver fir not only live for several years after the 

 butt is dissevered, but actually increase in bulk : thus 

 showing that the vital membrane, or that layer which 

 is always seated between the bark and the wood, 

 retains the power of enlarging itself, although there 

 ere no shoots to excite it into action, or outlet save 

 its own expansion. 



Attending to the development of a seedling plant, 

 we cannot fail to observe that there is a point 

 between the descending and ascending members 

 which seems peculiarly organised. Whatever enlarge- 

 ment or ramification of the axis takes place in the 

 first stage of the life, below this point, are roots, and 

 descend ; and whatever is above, are shoots, and rise 

 into the air. This point bears the cotyledons, or 

 seed-leaves ; it is the crown of the roots and the base 

 of the stem. In bulbs it is called the radical plate, 

 fig. 6 ; of herbaceous plants it is the crown, fig 7 ; 

 and of trees and shrubs it is called the life-knot, or 

 collet, fig. 8. 



This member is constitutionally of the greatest 

 importance in the system ; all the other members of 

 the plant may be destroyed or separated, without 

 risk of killing the plant, if the collet only be pre- 

 served. In some cases it may be divided into many 

 parts, each of which will become perfect plants. 

 Every scale of the bulbs of the common white and 

 orange lilies-, if pulled off with ever so small a portion 

 of the radical plate attached, will each, if placed in 

 the ground, become entire plants. In all bulbs, many 

 tubers, and all other herbaceous plants which have 

 not under-ground stems, the radical plate or crown 

 is the centre of vitality, from whence all accretion, 



whether of roots, stems or leaves, proceed. All the 

 productions of former years arose from it, and have; 

 withered away ; and all that shall be produced must, 

 spring from that slender body the radical plate of 

 a hyacinth or tulip bulb. 



Fig. 8. Fig. -. Fig, y. Fig. 6. 



Sections of different Plants, to show the Collet. 



If we examine this wonderfftl member we find it a 

 homogeneous, solid substance ; not gramilous as we 

 may suspect it to be, like the ovarium of an animal ; 

 but from its power or property of throwing ofl' an 

 endless train of perfect individual plants, we must 

 consider it to be an aggregation of vital gems which 

 are developed in the order of their position. The 

 most central bud or gem generally takes the lead ; 

 but if this be damaged or checked by accident, or if 

 it cannot appropriate the whole of the vigour derived 

 at any one time from the roots, the next gem in 

 order will be advanced, and perhaps one, two, or 

 three of the lateral gems will be ejected, these when 

 they do so appear, are called off-sets. In every year 

 of the existence of a bulb we see the radical plate 

 produce new roots, leaves, flowers, and seeds, all of 

 which when the last are ripe, fall off, and are for ever 

 separated from the mother plant. A successor in 

 the mean time comes forth, occupies the space of the 

 former, and is matured by the summer heat to be 

 fully developed in the following year. In this way 

 is the plant perennial, from its principal member being 

 a source whence flows in infinite succession its annual 

 products ; and so it continues to do, as long as the 

 plant remains in a sound and healthy state. Herba- 

 ceous plants in general not only produce an annual 

 rowth of leaves, flowers, and seeds, but also vivipa- 

 rous progeny parted off from the edges of the crown, 

 which however is not thereby diminished, as is the 

 case with the narcissus. Others, when they are sur- 

 rounded by numerous offsets die off, leaving the space 

 to be occupied by their offspring : of this description 

 is the strawberry. 



In many kinds of trees, especially those which 

 have buds situated on, and which send up suckers 

 from the roots, the collet becomes merged in -the 

 trunk and no longer conspicuous. In others it may 

 always be identified as being more swollen than that 

 part of the stem immediately above it. In the plant 

 called elephant's tongue (Testudinaria elepliant'ipex], 

 the great body of the plant is only an uncommonly 

 enlarged collet or ligneous tuber, fig. 9. 



Of the Stem or Trunk. The stem or axis of a plant 

 is that columnar body, which if above ground, serves 

 to support and elevate the fructification. It assumes 

 many forms and characters, as to bulk, structure, 



