16 



HISTORY OF THE VEGETABLE KINGDOM, 





and very close, as in the heaths. The internal 

 structure of roots very closely resembles that 

 of the stem, and shall he described along with 

 that organ. 



According to the general laws of vegetable 

 growth, plants of the same species are funiished 

 with the same species of root, not producing at 

 one time a woody or fibrous root, and at another 

 a bulbous root. Yet some exceptions to this rule 

 occur. If part of the root of 

 a tree planted by u, pond or 

 river, is accidentally laid bare 

 on the side next the water, or 

 if in the regular course of its 

 growth it protrudes beyond 

 the bank, so as to be now par- 

 tially immersed, the future de- 

 velopment of the part is considerably affected ; 

 for the root, which was fonnerly firm and woody, 

 instead of augmenting in the regular way by 

 the accession of new layers between the wood 

 and bark, thus enlarging the mass, divides now 

 at the extremity into many ramifications, or 

 sends out a num.ber of fibres from the surface, 

 which become again subdivided into fibres still 

 more minute, and gives to the whole an appear- 

 ance- something like a foxe's tail, m. This may be 

 seen in willows, growing beside ponds. On the 

 other hand, the phlevm pratense, when growing in 

 its natural moist soil, has a fibrous root ; but when 

 in a dry soil, where it is not unfrequently found, 

 the root is bulbous. The roots of utricularia 

 minor, exhibit curious appendages of small 

 membranous bladders attached to their slender 

 filaments, containing a transparent fluid and a 

 bubble of air, by means of which the plant is kept 

 floating in the water. If a slice of the beet 

 root be examined when the plant is a year old, 

 it wiU exhibit from five to eight concentric circles 

 of tubes or sap vessels, imbedded at regular in- 

 tervals in its pulp ; whereas other biennial roots 

 foi-m only one circle for each year, and are con- 

 sequently furnished at no time with more than 

 two. 



The most singular circumstance regarding roots, 

 however, is that they may be transformed into 

 stems, by inverting the plant. Thus, if the 

 stem of a young plum or cherry tree, or of a 

 wiUow, is taken in autumn, and bent so as that 

 one half of the top may be laid in the earth, 

 one half of the root being at the same time 

 taken carefully out, but sheltered at first from 

 the cold, and then gradually exposed to it ; and 

 the remaining part of the top and root subjected 

 to the same process in the following year, the 

 branches of the top wiU become roots, and the 

 ramifications of the root will become branches, 

 protruding leaves, flowers, and fruit in their 

 season. 



Use of roots. In the first place, as regards 

 the plant itself, the use of the roots is to serve 



as a means of attachment to it in the soil, 

 and to draw from thence a portion of the juices 

 necessary for its life and nourishment. The 

 roots of many plants appear to perfoi-m only 

 the first of these functions. This is chiefly re- 

 markable in thick succulent plants, which ab- 

 sorb from the air the substances necessary for 

 their nutrition at all points of their surface ; in 

 this case, these roots serve simply to fix the plants 

 to the soil. The magnificent cactus Peruvianus, 

 growing in the hot house of the museum of 

 natural histor'y at Paris, is of an extraordinary 

 height, and sends out its large branches with 

 extreme vigour, and often with amazing rapidity; 

 yet its roots are contained in a box which barely 

 holds four cubic feet of earth, which is never re- 

 renewed or watered. Some otherplants of thesame 

 nature maybe suspended by a thread to the ceiUng, 

 and they will grow without any earth at all, 

 merely by absorbing their nourishment from the 

 atmosphere. Neither are the roots of plants 

 always in proportion to the strength or size of 

 the trunks which they support. The tribe of 

 palms and pines, whose trunks sometimes reach 

 the height of a hundred feet and upwards, have 

 very short roots, wliich do not extend far in the 

 ground, and attach themselves but feebly to it. 

 On the contrary, herbaceous plants, whose weak 

 and slender stems die yeaidy, have sometimes 

 roots of gi-eat length and size compared with 

 the stem, as is the case in the hquorice shrub, 

 lucem, and the common weed called rest-harrow. 

 In general, however, roots extract from the eai'th 

 the substances which contribute to the growth 

 of the plant. All parts of the root, however, 

 do not equally perform this office, which is 

 accomplished chiefly, if not solely, by the ex- 

 tremities of the small fibres. It has been found 

 that their extremities are terminated by little 

 spongy bodies, called ampullce or spongiolcs, with 

 porous absorbing mouths. Dutrochet has min- 

 utely described these spongioles, which may be 

 seen by the aid of a microscope, attached as little 

 bags or knobs, to the minute fibres of the roots, 

 as seen at a a in the wood cut. 

 With a high magnifying power, 

 hexagonal cells are visible, covered 

 by a porous cuticle. The small 

 bulb at the extremity of the 

 root of the common duck weed, 

 affords a good example of these 

 spongioles. Whatever be their 

 structure, Dutrochet thinks, ab- 

 sorption is performed by those 

 extremities alone; and the truth of this may 

 be established by a simple experiment. It 

 we take a radish or turnip, and immerse in water 

 the small root by which the bulb is terminated, 

 it will vegetate and shoot forth leaves. On the 

 contrary, if it be so placed in the water that its 

 Ijvver extremity is not immersed, it gives no 



