HANTS'. 
445 
those of the flower. The greater number of 
plants close, either partly or entirely, their 
petals towards night, or on the approach of 
cold or wet weather. The hedysarum gy- 
rans whirls its leaves in various directions, 
when the air is still, by an apparently volun- 
tary effort. The dionasa muscipuia, Venus’s 
fly-trap, closes its leaves from the stimulus 
of insects which crawl upon them, and 
pierces them with its prickles. The phe- 
nomena of the common sensitive plant, the 
most distant branches of which close their 
leaves on any violence being offered to any 
part of it, are commonly known and ad- 
mired. Whether these appearances are the 
consequences of sensation in the vegetable, 
it is impossible to determine ; but they are 
so simkar to what we observe in animated 
beings, that the term sensitive plant is very 
appropriate. If the distant parts of the plant 
are aiiected through the medium of nerves, 
their action seems to be much less quick than 
those of animals, as the half or the whole of 
a minute generally elapses in this, climate 
before the whole of the plant droops, but 
it is said to be otherwise in their native cli- 
mate. 
Fluids of plants. As the true coarse of 
the fluids in animals, and the power by 
which the circulation is performed, are mo- 
dern discoveries, so we have still to learn a 
satisfactory explanation of the corresponding 
circumstances in vegetable life, 1 hat the 
juices of plants pass from one part to another, 
admits of no doubt ; but the observations of 
naturalists have been so various and incon- 
sistent, that no theory can be framed suffi- 
ciently comprehensive to embrace their se- 
veral conclusions. It may indeed be con- 
cluded, that as the life of a vegetable is more 
obscure, so we cannot expect the same en- 
ergy of action which is manifested in the cir- 
culating organs of animals. 
It is manifest tto common observation, that 
there does not e?xist the same intimate union 
between tie different parts ol a Vegetable as 
we find be ween those of animals: different 
parts of th» same plant will put forth leaves 
and ripen fruit at very different seasons of 
the year, according to the particular tempe- 
rature in which each branch is placed. A 
branch of a vine introduced into a hot-house 
will vegetate in the midst of winter; while 
the rest ol the plant, which remains exposed 
to the vicissitudes of the climate, will evince 
little or no sympathy. We know of nothing 
like this in the animal kingdom, and there- 
fore it seems reasonable to conclude that 
there is not in a vegetable any thing analo- 
gous to a heart, from and to which, as a com- 
mon centre, its fluids are directed. 
It has been assumed by many botanists, 
that there is a succus communis, or universal 
sap, differing little from water, and the same 
in all plants. It seems more consonant, how- 
ever, to observation, to conclude that the 
fluids differ in different genera of vegetables. 
There is an infinite variety in the obvious 
properties of the juices of plants, some of 
which, in lead of resembling water, are more 
of the consistency of milk. Grafts only grow 
on kindred stocks, which may reasonably be 
attributed to an unfitness of the juices of other 
genera of plants. 
With respect to what has been called the 
succus proprius of plants, which alone has 
been said to differ in different plants, it seems 
to be nothing more than the product of a pro- 
cess analogous to that of secretion in animals ; 
thus a plant of mint nourished by water alone, 
will still elaborate,, by its vegetative power, 
an essential oil peculiar in odour to its own 
species. 
The juices of many plants abound so much 
in a mucilaginous and saccharine principle as 
to be fermentable. The sap of the birch-tree 
drawn in spring by tapping has been long 
employed to make wine. A species of the 
maple affords sugar; but no plant abounds 
so much in this vegetable product as the 
sugar-cane. The mucilaginous or gummy 
principle prevails more particularly in the dif- 
ferent sorts of plum. By the experiment- on 
the sap-wood of the oak, related above, it ap- 
pears that there are both sugar and mucilage 
in the juices of a tree remarkable for its bit- 
terness. 
Mucilage and sugar seem to exist diffused 
in the general mass of fluids in vegetables ; 
on the other hand, turpentine, resin, express- 
ed and essential oil, and what is called the ex- 
tractive principle, seem to be the product of 
secretion ; but the fluids deposited in cists 
are so often necessarily mixed with the other 
juices, by the processes of extraction, that 
there must remain considerable doubt as to 
the accuracy of this particular distribution. 
It may generally be remarked, that the pro- 
ducts of secretion in plants are of an inflam- 
mable nature. The seeds of plants generally 
abound in a heavy oil which may be obtained 
by pressure, such as oil of almonds, linseed, 
and palma christi or castor oil. The essen- 
tial oils, or those obtained by distillation, 
are in general extremely acrid; so much so, 
that they produce a wound when inadvert- 
ently applied to the tongue in an undiluted 
state. Oil of cloves is employed to destroy 
the exposed nerve in decaying teeth, in order 
to cure the tooth-ache; but its use requires 
considerable caution, as it is liable to injure 
the teeth adjoining to that which is diseased. 
The bitter, narcotic, and acid principles, are 
also to be considered as the products of se- 
cretion. 
Few questions have excited greater atten- 
tion than those respecting the course of the 
fluids in vegetables. When wounds have 
been made in trees, it is found that the sap 
flows more copiously from the upper side, or 
that part of the wound which is nearest the 
branches. From whatever cause this may 
proceed, it seems to be intimately united 
with another fact. If a wound is made 
through the bark of a growing tree, the effort 
which takes place to heal the wound is fnade 
from above. The lower lip of the wound 
remains shrivelled and inactive; and if the 
wound has been extensive, seems from year 
to year rather to suffer decay ; the upper lip, 
on the contrary, becomes turgid, and extends 
itself downwards to repair the breach. This 
effort is particularly remarkable in wood 
wliichhas suffered compression from the em- 
braces of the honeysuckle. Dr. Darwin, in 
his Phytologia, attempts to explain this and 
many other phenomena by the ingenious 
idea, tlrnt a tree is a complex being com- 
posed of many individuals; for he considers 
every bud of a tree as having an independant 
vegetative power/ The effort above-men- 
tioned he considers as caused by the buds of 
the tree sending down their vessels, and pro- 
pelling their fluids towards the root, h et it 
seems generally to have been concluded, that 
the sap rises upwards in the spring from the 
root towards the branches. Early in the sea- 
son Dr. Hope made incisions of different al- 
titudes into the root and stem of a birch. As 
tiie sap rose, it first flowed from the superior 
margin of the lowest incision, and then in •re- 
gular succession, from the upper margins of 
the other incisions, till at last it reached the 
highest. It does not appear’, however, to be- 
satisfactorily ascertained whether the sap in 
this experiment proceeded from the root, or 
whether it was successively put in motion 
higher and higher as the process ot vegeta- 
tion took place; lor the upper parts of a tree 
are more exposed to cold, and vegetation 
may on that account be retarded. Dr. ilales 
cut off the stems of vines in the spring, and 
then by fixing tubes on the stumps, was able- 
to ascertain with what force the sap was pro- 
pelled. In some trials the sap rose to the 
height of 35 feet. Tubes have been fixed to 
the large arteries of animals, as near as pos- 
sible to the heart, in which the blood did not 
rise higher than nine feet. 
Such being the force with which the juices 
of vegetables are propelled, it can scarcely 
be doubted that their sap is contained in ves- 
sels. Yet differences of opinion have arisen 
even as to this particular; and as the vessels 
of vegetables have not been satisfactorily 
traced, it has been advanced that there exists 
no other circulation than a transmission of 
fluids through cellular substance. A circula- 
tion, however, so vigorous as that of a thriv- 
ing vegetable, cannot be conceived to be con- 
ducted, except through a limited and well de- 
fined channel. It must be confessed, that 
considerable difficulties attend this inquiry ; 
but the existence of vessels, at least in the 
leaves of plants, is proved by the following 
simple experiment, which may be satisfacto- 
rily tried on plants having coloured sap 
Tear asunder a fig-leaf, for instance, and the 
white fluid will be observed to flow from cer- 
tain points which are doubtless the extremi- 
ties of broken vessels. 
From the experiments of Dr. Hales above- 
mentioned it appears, that the sap of the vine 
rose in a tube to 35 feet, or about the same 
Height as a column of water equal in weight 
to the atmosphere. The pressure of the at- 
mosphere is known to assist animals in suck- 
ling ; and whether some modification of the- 
same power may not assist vegetable absorp- 
tion, may be the subject of future inquiry. 
Dr. Hales, in his statical experiments, . 
mentions several, in which he tried to change 
the natural flavour of fruits, and to commu- 
nicate those of several spirituous liquors, and 
of different odoriferous infusions. With this 
intention he plunged in different liquors 
branches loaded with fruit, and left them 
there for some time, without being able to 
perceive that the taste of the fruits was in the 
least altered, whether the experiment was 
made upon them ripe or unripe. But he 
almost always perceived the smelt of the'li- 
quors or infusions in the stalks ot the leaves, . 
and in the wood. Fie conjectures, with much ; 
probability, that the vessels near the fruit 
become so fine as not to admit the odoriferous 
particles. 
M. Ronnet made experiments on flowers , 
similar to those which -Dr. Mates made on 
fruits. He chose such' flowers as have nat«- 
