PLANT. 



the latter spring the root and radicles. 

 The position of the corcle in the seed, 

 which is always in the vicinity of the eye, 

 is a cicatrix, or umbilicus, remaining af- 

 ter the separation of the funis from the 

 pericarp, to which the seed has been at- 

 tached. The first radicle elongates, and 

 pushes into the earth, before the plumule 

 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 wa- 

 ter. Hence originates the root, the most 

 important part of the plant. The solid 

 parts of the trunk of the plant are the 

 cortex, or outer bark ; the liber, or inner 

 bark; the alburnum, or softwood; lig- 

 num, or hard wood ; und medulla, or pith. 

 These lie in concentric circles ; and the 

 trunk enlarges, by the formation of a new 

 liber, or inner bark, every year ; the 

 whole of the liber, excepting indeed its 

 outermost layer, which is transformed 

 into cortex, becoming the alburnum of 

 the next, and the alburnum becoming 

 the lignum. Hence a mark of any sort, 

 as the initials of a name, which has pene- 

 trated through the outer into the inner 

 bark, must in a long process of years be 

 transferred to the central parts of the 

 trunk. Independently of these more so- 

 lid parts of the trunk, we generally meet 

 with some portion of parenchyma and 

 cellular substance : the vessels contained 

 in this may be compared to arteries and 

 veins, air vessels, and lymphatics. The 

 lymphatics lie immediately under the cu- 

 ticle, and in the cuticle, and by branching 

 different ways are enabled to perform 

 the alternating economy of inhalation and 

 exhalation : below these lie the arteries, 

 which rise immediately from the root, 

 and communicate nutriment in a perpen- 

 dicular direction : interior to these lie 

 the reducent vessels, or veins, which are 

 softer and more numerous, and in young 

 shoots run down through the cellular 

 texture and the pith. Between the ar- 

 teries and veins are situated the air- 

 vessels. 



" The lymphatics of a plant may be 

 often seen with great ease by merely strip- 

 ping off the cuticle with a delicate hand, 

 and then subjecting it to a microscope ; 

 and in the course of the examination, we 

 are also frequently able to trace the ex- 

 istence of a great multitude of valves, by 

 the action of which the apertures of the 

 lymphatics are commonly found closed. 

 Whether the other systems of vegeta- 

 ble vessels possess the same mechanism, 



VOL. V. 



we have not been able to determine de- 

 cisively : the following experiment, how. 

 ever, should induce us to conclude that 

 they do. If we take the stem of a com- 

 mon balsamine, or of various other plants, 

 and cut it horizontally at its lower end, 

 and plunge it, so cut, into a decoction 

 of Brazil wood or any other coloured 

 fluid, we shall perceive that the arteries, 

 or adducent vessels, as also the air ves- 

 sels, will become filled or injected by an 

 absorption of the coloured liquor, but 

 that the veins, or reducent vessels,, will 

 not become filled ; of course evincing an 

 obstacle in thi- direction to the ascent of 

 the coloured fluid. But if we invert the 

 stem, and in like manner cut horizontally 

 the extvemity which till now was upper- 

 most, and plunge it so cut into the same 

 fluid, we shall then perceive that the 

 veins will become injected, or suffer the 

 fluid to ascend ; but that the arteries will 

 not : proving clearly the same kind of 

 obstacle in the course of the arteries in 

 this direction, which was proved to ex- 

 ist in the veins in the opposite direction ; 

 and which reverse obstacles we an 

 scarcely ascribe to any other cause than 

 the existence of valves. 



" By this double set of vessels, more- 

 over, possessed of an opposite power, and 

 acting in an opposite direction, the one 

 to convey the sap or vegetable blood for- 

 wards, and the other to bring it back- 

 wards, we are able very sufficiently to 

 establish the phenomenon of a circulatory 

 system." 



The author admits that no experiments, 

 nor observations, have been able to de- 

 tect the existence of muscular or nervous 

 fibres in vegetables ; but notwithstanding 

 this, in answer to those who maintain the 

 necessity of a regular and alternate con- 

 traction and dilatation for the production 

 of a circulatory system, both in animals 

 and vegetables, he says, " still must we 

 admit the competency of other powers to 

 produce the same result, while we reflect 

 on the facility with which the human cutis 

 or skin, an organ destitute of all muscu- 

 lar fibres whatever, contracts and relaxes 

 generally on the application of a variety 

 of other powers ; powers different in their 

 nature, and in their effect palpable to the 

 external senses : whilst we recal to mind 

 that it is contracted by austere, and re- 

 laxed by oleaginous preparations ; con- 

 stringed by cold, and dilated by warmth : 

 and that the opposite passions of the mind 

 have a still more powerful influence on 

 the same organ, since fear, apprehension, 

 horror, will not only freeze and corrugate 



