4 - 1(3 
rally little perfume, as the different species of 
French beans. Stems with these flowers were 
immersed in tubes, some of which were filled 
with spirit of wine, others with Hungary 
water, & c. In about 24 hours the flowers 
were laded, and they had already acquired 
in a very sensible degree the odours of the 
liquors which they had imbibed. The odour 
became much more remarkable a few days 
afterwards. M. Bonnet also found that the 
leaves of the apricot-tree acquired a sen ible 
odour from the liquors into which branches 
of that tree were plunged. 
Functions of plants. The leaves of plants 
have been not improperly compared with 
the lungs of animals. “ Plants, as well as 
animals,” says an author whom we have al rea - 
dy quoted with approbation, “ perspire, and 
in both cases this function is essential to 
health. By the experiments of Dr. Hales 
and M. Guettard, it appears that the perspi- 
rable matter of vegetables differs in no re- 
spect from pure water, excepting that it be- 
comes rather sooner putrid. The quantity 
perspired varies, according to the extent of 
the surface from which it is emitted, the tem- 
perature of the air, the time of the day, and 
the humidity of the atmosphere. As the 
leaves form the greatest part of the surface, it 
is natural to suppose, that the quantity of 
these will very materially affect the quantity 
of the perspiration. Accordingly, the expe- 
riments of Dr. Hales have ascertained, that 
the perspiration of vegetables is increased or 
diminished, chiefly in proportion to the in- 
crease or diminution of their foliage. The 
degree of heat in which the plant was kept, 
according to t he same author, varied the 
quantity of matter perspired; this being 
greater, in proportion to the greater heat of 
the surrounding atmosphere. The degree of 
light has likewise considerable influence in 
this respect; for Mr. Philip Miller’s experi- 
ments prove, that plants uniformly perspire 
most in the forenoon, though the temperature 
of the air in which they are placed should 
be unvaried. M. Guettard likewise informs 
us, that a plant exposed to the rays of the sun 
has its perspiration increased to a much 
greater degree, than if it had been exposed to 
the same heat under the shade. Finally, the 
perspiration of vegetables is increased in pro- 
portion as the atmosphere is dry, or in other 
words, diminished in proportion as the atmo- 
sphere is humid.” 
Dr. Hales found that a sun-flower, weigh- 
ing three pounds, perspired 22 ounce's during 
24 hours. Dr. Keil perspired 31 ounces in 
24 hours. The quantity therefore perspired 
by the sun-flower was muen greater, in pro- 
portion to its weight, than that perspired 
front the human body. Dr. Keil ate and 
drank tour pounds ten ounces in 24 hours. 
Seventeen times more nourishment was taken 
in bv the root of the sun-flower, than was 
taken in by the man. If the perspiration of 
vegetables is checked, they speedily fade. It 
is checked from glutinous substances adher- 
ing to their surface : hence the advantage of 
washing them. The more healthy and vigo- 
rous the plant, the more copious the perspira- 
tion ; though an excess, us well as a defect of 
it, seems prejudicial and even destructive to 
vegetables. It bears also a proportion to the 
quantity of leaves, these being the principal 
ergans of perspiration. 
The odoriferous exhalation of leaves and 
PLANTS. 
flowers forms an atmosphere round vege- i 
tables, which strikes our senses, and 'which 
the contact of a body on lire is sometimes 
capable of inflaming, as has been observed 
with regard to the tiaxineila. 
The experiments of Dr. Priestley have 
sufficiently shewn that vegetables have the 
power of correcting bad air ; and Dr. Ing'en- 
liouz has proved that they have the faculty 
of producing oxygen gas, only when acted on 
by the rays of light. If a vegetable is im- 
mersed in water, and the rays of the sun di- 
rected on it, air-bubbles will be observed to 
collect on the leaves, and at length rise to 
t he surface of the water. This appearance 
is most remarkable in the morning, as the 
leaves have not then been previously ex- 
hausted by the action of light. Oxygen air 
of a great degree of purity may be obtained 
in the summer time, by inverting a jar tilled 
with water in such a manner as to receive 
the air-bubbles as they arise. All plants, 
however, do not emit this air with the same 
facility ; there are some which emit it the 
moment- the rays of the sun act upon them, 
and this is the case with lavender. Some 
aquatic plants afford oxygen air with great 
facility, some more slowly, hut none later 
than eight or ten minutes, provided the sun’s 
light is strong. The air is almost entirely 
furnished bv the inferior surface of the leaves 
of trees ; herbaceous plants afford it from 
almost the whole of their surface. The 
leaves afford more air when attached to the 
plant, than when gathered ; and the quantity 
is greater, the fresher and sounder they are. 
Young leaves afford but a small quantity of 
oxygen air; those which are full grown af- 
ford more, and the more the greener they 
are. The epidermis, the bark, and petals, 
do not afford it, and in general oxygen pro- 
ceeds only from those parts of plants which 
are of a green colour. Thus green corn and 
green fruits afford this air, but it is not pro- 
duced by those which are ripe ; and flowers 
in general render the air noxious. These 
facts may serve to explain the manner in 
which the light of the sun operates in ma- 
turing fruits, viz. by expelling the super- 
fluous oxygen, .and thus changing them from 
a harsh and sour, into a mild and sweet sub- 
stance. Aquatic plants, and such as grow 
in moist places, are remarkable not only for 
affording a large quantity of oxygen gas, but 
also for absorbing hydrogen gas, and are 
therefore in all respects calculated for puri- 
fying the air of marshy situations. A very 
extraordinary pow'er of absorbing hydrogen 
air was observed in the willow by Dr. Priest- 
ley; and this fact seems connected with the 
rapid growth of that plant in marshy situa- 
tions, where much of this air is produced. 
M. Sennabier found that plants yield much 
more oxygen air in distilled water impreg- 
nated with carbonic acid gas, than in simple 
distilled water. 
It appears further, from the experiments 
of Dr. Priestley, that plants will bear a greater 
proportion of hydrogen than of carbonic acid 
air, and that oxygen gas appeared generally 
injurious to plants. A sprig of mint growing 
in water, placed over a fermenting liquor, and 
of course exposed to carbonic acid air, be- 
came quite dead in one day ; a red rose be- 
came of a purple colour in-24 ho rs. Plants 
die very soon both in nitrous air, and in com- 
mon air when saturated with it. Air appears 
j uniformly to have been purified by healthy 
plants vegetating in it; but these experi- 
ments require great nicety, a- the least de- 
gree of putrefaction will injure the air. The 
air contained in the bladders of marine plants 
was found considerably purer than common 
air. 
Atmospheric air is restored, after being 
injured by respiration or combustion, by a 
plant Vegetating in it. This restoration of 
air depends upon the vegetating state of the 
plant; for a number oi mint-leaves fresh-ga- 
thered being kept in air in which candles had 
burnt out, did not restore the air. Any plant 
will effect this purpose, but those ot the 
quickest growth in the most expeditious man- 
ner. 
That plants have a property of producing 
pure air from water, is evident from an ex- 
periment of Dr. IViestley’s. The green 
matter which is to be observed in water is 
doubtless a vegetable production. Water 
containing this green matter always afforded 
oxygen 'air in a large quantity; but water 
which had it not afforded none. It has been 
frequently observed that vegetables do not 
thrive in the dark. A receiver was therefore 
tilled with water, and kept till it was in a 
state of giving air copiously; after this it 
was removed into a dark room, and from that 
time the production of air entirely ceased. 
When placed again in the sun, it afforded 
no air till about ten days after, when it had 
more green matter ; the former plants being 
probably all dead, and no air could be pro- 
duced till new ones were formed. 
From various experiments it appeared that 
different animal and vegetable putrescent 
substances afforded a very copious pabulum 
for this green vegetable matter, which pro- 
duced so freely the oxygen air; whence the 
philosophic author of this discovery is led to 
the following conclusions : “ It is impossible,’' 
says he, “ not to observe from these experi- 
ments the admirable provision in nature, to 
prevent or lessen the fatal effects of putre- 
faction ; especially in hot countries, where the 
rays of the sun are most direct, and the heat 
most intense. Animal and vegetable sub- 
stances, by simply putrefying, would neces- 
sarily taint great masses of air, and render 
it unfit for respiration, did not the same sub- 
stances, putrefying in water, supply a most 
abundant pabulum for this wonderful vege- 
table substance, the seeds of which seem to 
exist throughout the atmosphere. By these 
means, instead of the -atmosphere being cor- 
rupted, a large quantity of the purest air is 
continually thrown into it. By the same 
means also, stagnant waters are rendered 
much less offensive and unwholesome than 
they would otherwise be. That froth which 
we observe on the surface of such waters, 
and which is apt to excite disgust, generally 
consists of the purest air, supplied by aquatic 
plants. When the sun shines, this air may- 
be observed to issue from them. Even when 
animal and vegetable substances putrefy in 
air, as they have generally some moisture in 
them, various other vegetable productions, 
in the form of mold, &c. find a propel nutri- 
ment in them, and by converting a consi- 
derable part of the noxious effluvia into their 
own substance, arrest it in its progress to cor- 
rupt the atmosphere,” 
The same vegetables which afford oxygen 
