PLANT. 
dicle elongates, and pnslies into the earth, 
before the pluimile evinces any ciiange ; 
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, 
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 soft wood ; lignum, 
or hard wood ; and medulla, or pith. These 
lie in concentric circles ; and the trunk en- 
larges, by the formation of a new liber, or 
inner bark, every year ; tire 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 
penetrated 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 solid parts of 
the trunk, we generally meet with some 
portion of parenchyma and cellular sub- 
tance : the vessels contained in this may be 
compared to arteries and veins, air vessels 
and lymphatics. The lymphatics lie imme- 
diately under the cuticle, and in the cuticle, 
and by branching different ways are enabled 
to perform the alternating economy of inha- 
lation and exhalation ; below these lie tlie 
arteries, which rise immediately from the 
root, and communicate nutriment in a per- 
pendicular 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 tex- 
ture and tlie pith. Between the arteries 
and veins are situated the air-vessels. 
“ The lymphatics of a plant may be often 
seen with great ease by merely stripping off 
the cuticle with a delicate hand, and then 
subjecting it to a microscope; and in the 
course of the examination we are also fre- 
quently able to trace the existence 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 vegetable vessels possess 
the same mechanism, we have nat been 
able to determine decisively; the following 
experiment, however, should induce us to 
conclude that they do. If we take the stem 
of a common balsamine, or of various other 
plants, and cut it horizontally at its lower 
end, and plunge it, 50 cut, into a decoction 
of Brazil wood, or any other coloured fluid; 
we shall perceive that the arteries, or addu- 
cent vessels, as also the air vessels, will be- 
come 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 this direction 
to the ascent of the coloured fluid. But if 
we invert the stem, and in like manner cut 
horizontally the extremity which till now 
was uppermost, and plunge it so cut into 
the same fluid, we shall tlien 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 ob- 
stacle in the course of the arteries in this 
direction, which w’as proved to exist in tlie 
veins in the opposite direction ; and which 
reverse obstacles we can scarcely ascribe to 
any other cause than the existence of valves. 
“ By this double set of vessels, moreover, 
possessed of an opposite power, and acting 
in an opposite direction, the one to convey 
the sap or vegetable blood forwards, and 
the other to bring it backwards, we are 
able very sufficiently to establish the pheno- 
menon of a circulatory system.” 
The author admits that no experiments, 
nor observations, have been able to detect 
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 contraction 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 muscular fibres whatever, contracts and 
relaxes generally on the application of a 
variety of other pov/ers; powers different 
in their nature, and in their effect palpable 
to the external senses : whilst we recal tn 
mind that it is contracted by austere, and 
relaxed by oleaguwus preparations ; con- 
stringed by cold, and dilated by warmth ; 
and that the opposite passions of the mind 
have a still more pow erful influence on the 
same organ, since fear, apprehension, horror, 
will not only freeze and corrugate the skin, 
but in the language of the poet, which is 
also the language of nature, freeze the blood 
itself, making 
‘ each particular hair to stand on end 
Like qnills upon the fretful porcupine 
while hope, pleasure, agreeable expecta- 
tion, smooth, soften, and expand it to an 
