PLANTS. 
air very plentifully in the light of the sun, 
atibrd in the shade air less pure than that of the 
atmosphere. This striking effect of light on 
vegetables is a strong argument in favour ot 
the opinion, that the motion of the juices of 
vegetables is performed by vessels, which, 
like those of animals, possess irritability, and 
are excited to action by stimulating sub- 
stances. 
The effect of vegetation in producing the 
oxygen air which was afforded in the pre- 
ceding experiments, seemed in some mea- 
sure dubious to count Rumford, who extract- 
ed vital air bv immersing in water a variety 
of substances,' as raw silk, cotton, wool, eider- 
down, hare’s fur, sheep’s wool, ra.vellings of 
linen, and human hair. He was led, from the 
result of these trials, to suspect that the pure 
air was merely separated from the water ; and 
that any substance which would act by a ca- 
pillary attraction, so as to separate the com- 
ponent parts of the water, would effect the 
production of pure air. He therefore pro- 
cured a quantity of spun glass, which con- 
sists of minute tubes, and immersed it in wa- 
ter, but the quantity of pure air produced 
was very trifling. Hence he concludes, that 
there is something in those substances which 
operates in producing pure air, and that it is 
not merely a mechanical separation of the 
component parts of water. 
The light of lamps produced the same ef- 
fect as the sun’s light ; air in great quantities 
was produced, and perfectly pure. Vege- 
tables will also, with any strong light, pro- 
duce oxygen air as well as with the light of 
the sun.' The air from silk was much supe- 
rior to that from vegetables. 
Plants have a remarkable sensibility to 
lhht; they unfold their flowers to the sun, 
they follow his course by turning on their 
stems, and are closed as soon as he disap- 
pears. Vegetables placed in rooms where 
they receive light only in one direction, al- 
ways extend themselves that way. If they 
receive lie-lit in two directions, they direct 
their course towards the strongest. Trees 
growing in thick forests, where they only re- 
ceive light from above, direct their shoots 
almost invariably upwards, and therefore be- 
come much taller and less spreading than 
such as stand single. This affection for light 
seems to explain the upright growth of vege- 
tables, a curious phenomenon, too common 
to be much attended to. It has been ascer- 
tained by repeated experiments, that the 
green colour of plants is entirely owing to 
light; for plants feared in the dark are well 
known to be perfectly white. 
If we take a succulent plant, and express 
its juice, the liquor appears at iitst uniformly 
green; but allow it to stand, and the greeji 
colour separates from the watery lluid, and 
falls to the bottom in a sediment. If we col- 
lect this sediment it will be found to be of an 
oily nature, for it does not dissolve in water ; 
but it will in spirit of wine, or oil, to which it 
imparts a green colour. As the sun pro- 
duces the. green colour in plants, and as this 
resides in an oily matter, it was formerly I 
concluded that light produces the oily matter 
of vegetables, and that it effects this by fur- 
nishing the principle of inflammability. The 
new chemical doctrines, however, afford a 
much more satisfactory explanation of the j 
effect of the sun’s rays m producing the oily i 
matter in vegetables. Vegetable matter con- 
sists in general of carbon, hydrogen, and ox- 
ygen; die sun’s ray produce a disengage- 
ment of the latter principle in the form ol 
vital air, and the two former are the consti- 
tuent principles of oil. 
M. Bonnet made a series of experiments 
in order to ascertain whether the superior or 
the inferior surfaces of leaves have a. greater 
share in performing perspiration. From the 
trials which he made, he concludes that the 
inferior surface of the leaf is in general by 
far the most active in this respect, though in 
one or two species of vegetables this differ- 
ence was much less remarkable. 1 he mal- 
low was tiie only vegetable the leaves of 
which perspired more by the upper than the 
inferior surface. 1 he method which he em- 
ployed to ascertain the comparative ellect of 
tiie two surfaces was, to cover first one and 
then the other surface with oil. ff he leaves 
were then immersed in tubes filled with wa- 
ter, and the quantity of perspired matter was 
measured by the length of the tube emptied 
in a given time. The oil, by stopping up the 
pores, prevented perspiration from the sur- 
face to which it was applied. Some large 
leaves of the white mulberry-tree being 
kept suspended on water with their upper 
surfaces in contact with the fluid, faded in 
five days; some leaves of the same tree, 
being placed in a similar situation, but with 
the inferior surface touching the water, were 
preserved green for nearly six months. 
The sexual system has been the prevalent 
system of botany for many years. It is well 
known that the palm is of that class of vege- 
tables which has flowers of different sexes on 
different trees. The peasants in the Levant, 
whether acquainted with this fact, or whether 
directed to the practice by accident alone, 
have been accustomed to break branches 
from the male palm while in flower, and at- 
tach them to the female plant, which they 
find to be constantly productive of an abun- 
dant crop. This fact has also been proved 
by a most decisive experiment of M. Gled- 
itsch. There was in the royal garden at 
Berlin a beautiful palm-tree, a female plant, 
which, however, though 25 years old, had 
been always barren. There was another palm 
at Leipsic of the male kind, which blossomed 
every year. The ingenious botanist under- 
took to fecundate the palm at Berlin from 
that at Leipsic, and had some of the blos- 
soms conveyed by the post. '1 he conse- 
quence was, that he produced that season 
excellent dates; and the experiment, prose- 
cuted with some variation for several suc- 
ceeding years, was attended with the same 
success. 
It has been said, that the pollen was des- 
tined for the impregnation of the germen. 
This is performed in the following manner : 
1 he antherae, which at the first opening ot 
the flower are whole, burst soon after, and 
discharge the pollen. Being dispersed about 
the flower, part of the pollen lodges on the 
surface of the stigma, where it is detained by 
the moisture yvith which that part is covered. 
Each single grain or atom of the pollen has 
been observed by the microscrope to burst 
in this fluid, and is supposed to discharge 
something which impregnates the germen 
below. What the substance is which is so 
discharged, and whether it actually passes 
through the style into the germen, seem yet 
447 
undetermined, from fhe great difficulty of 
observing such minute parts and operations. 
In some vegetables, the stamina move to- 
wards the pistillum; and a very evident mo- 
tion of them is observed in the flowers of the 
common berberry, on touching them with 
the point of a pin. 
As vegetables, like animals, are liable to 
decline, and ultimately to perish by age, the 
offices of the parts of fructification are of the 
most important nature. If trees had been 
capable of increase only by grafts, layers, or 
cuttings, it seems probable that they would 
long ago have been lost. An ingenious and 
philosophical botanist, Mr. Knight, has par- 
ticularized several sorts of apples, which a 
century ago were extremely thriving and in 
high repute, some of which are at this time 
wholly lost, and others are in such a state 
of decline and imperfection as to be little 
esteemed. By the fertility ofseeds, however, 
new varieties of this as well as of all other 
fruits and trees are continually produced. 
A tree produced from a cutting exactly re- 
sembles the parent plant; not so one raised 
from a seed, which generally derives its 
origin from more than one parent, and 
in dioecious plants must- always do so. 
Hence the endless variety which interests the 
florist. When this cause is considered as 
having operated for ages, we cease to wonder 
at the diversified appearances which we ob- 
serve in a bed of seedling plants. Mr. Knight 
strongly advises to take grafts from indivi- 
1 duals lately raised from seeds, which he as- 
sures us possess a vigour of growth never met 
with in old varieties. Strawberries and po- 
tatoes also become unproductive, unless the 
old varieties are replaced by others raised 
from seed. 
The nourishment of vegetables, as it is so 
intimately connected with the important 
science of agriculture, has deservedly attract- 
ed considerable attention. Mr. Boyle dried 
in an oven a quantity of earth proper for ve- 
getation, and after carefully weighing it, 
planted in it the seed of a gourd; he watered 
it with pure rain-water, and it produced a 
plant which weighed fourteen pounds, though 
the earth had suffered no sensible diminu- 
tion. 
• A willow-tree was planted by Van Hel- 
mont in a pot containing 100 pounds of earth. 
This was in general watered with distilled 
water, or sometimes with rain-water which 
appeared perfectly pure. The vessel con- 
taining the plant was covered in such a man- 
ner as totally to exclude the entrance of all 
solid matter. At the end of five years, upon 
taking out the plant, he found it to have in- 
creased in weight not less than 119 pounds, 
though the earth had lost only two ounces of 
its original weight. 
These experiments would admit of some 
doubt, and must have remained in a great 
measure inexplicable, but for the experi- 
ments of Mr. Cavendish, and the facts re- 
lated by Dr. Priestley, which place it be- 
yond a doubt, that vegetables have a power 
of decomposing water, and converting it, 
with what they derive from the atmosphere, 
into almost all the different matters found to 
exist in their substance. 
All the proper juices of vegetables depend 
on the organization, as it is evident from the 
operation of grafting. From the materials of 
