October 3.] 
mouth and nostrils proceeds immediately to the lungs 
and acts upon the blood ; in plants, when it is inhaled 
by their leaves, it operates instantaneously upon the 
sap. The changes that take place have just been im- 
! perfectly noticed, and we have no space to do more than 
add, that the oxygen of the atmosphere is the gas essen¬ 
tial to the existence of animals; but it is its carbonic 
acid that is quite as important to vegetables. They 
may be considered the vital airs of the two classes. If 
animals are placed in a situation where they inhale pure 
oxygen, their functions are highly and rapidly increased; 
but it is an exhilaration which would soon terminate in 
exhaustion and death, if breathed by them for any ex¬ 
tended period. So plants will flourish in an atmosphere 
containing 1-12th of carbonic acid, but if it much 
exceeds this proportion, they are rapidly destroyed. 
During sleep, animals respire less carbonic acid than 
during their waking hours; so plants emit little or no 
oxygen during the night. 
After an animal has enjoyed the regular course of its 
functions for a period varying in its duration, the time 
at length arrives when decay commences. The wasted, 
enfeebled, and relaxed form gradually declines, until 
death finally closes all activity. The body then becomes 
contracted and rigid ; the skin changes the ruddy tinge 
of health for death’s pallid hue. Decomposition speedily 
ensues, with all its offensive phenomena; and finally, 
the only permanent remains are the skeleton and a 
small amount of earthy matter. The same characteris¬ 
tics attend the last period of vegetable existence. Plants 
may flourish only for one season, or their lives may be 
extended through centuries of years, yet decay eventually 
comes over them; becoming more and more stunted, 
weak, pallid, and ragged, they eventually cease to live, 
become contracted and rigid, and pass through the same 
phases of putrefaction that are exhibited by the animal 
carcass. In both there was a time when warmth and 
exposure to the atmosphere were the sources of vigour 
—these now become the agents of destruction; they 
were once able to resist and to overcome the laws of 
chemical affinity — they now are destroyed by their 
attacks. What causes this most striking change ? 
What antiseptic agent have they lost? There can be 
but one reply. It was their vitality. Now, let us examine 
how the vitality of plants in other respects resembles 
the vitality of animals, and we will confine this examin¬ 
ation to two or three points. 
Plants are excitable. Light acts upon them as a 
stimulus. Every body must have observed that plants 
bend towards the direction from whence its brightest 
influence proceeds. M. Bonnet, the French botanist, 
demonstrated this in some very satisfactory experiments, 
by which he showed that plants grown in a dark cellar 
all extended themselves towards a small orifice admitting 
a few rays of light. Every flower almost has a particu¬ 
lar degree of light requisite for its full expansion. The 
blossoms of tlie pea, and of other papilionaceous plants, 
spread out their wings in fine weather, to admit the 
solar rays, and again close them at the approach of 
3 
night. Plants requiring a powerful stimulus do not 
expand their flowers until noon, whilst some would be 
destroyed if compelled to open in the meridian sun. 
The night-blooming cereus unfolds its flowers only at 
night. Heat also acts as a stimulus upon plants. 
M. Duhamel observed, that during moderately fine wea¬ 
ther the foot-stalk of a leaf of the sensitive plant 
(■Mimosa pudica) stood in the morning at an angle with 
the lower part of the stem of 100°; at noon, the angle 
had increased to 112°, but at night had fallen to 90° 
If a leaflet of this plant be but slightly touched, it im¬ 
mediately shrinks away; and the impulse being commu¬ 
nicated, each pair of leaflets on the branch collapse in 
succession; and if the impulse be strong, the very 
branch itself will sink down by the side of the stem. 
If an insect alight upon the upper surface of the Venus’s 
fly-trap ( Dioncea musdpula), its sides spasmodically 
approach each other, and crush to death the intruder. 
If the inner side, near the base, of any one of the 
anthers of the barberry ( Berberis vulgaris) be gently 
touched, as with a bristle or feather, it instantly springs 
forward and strikes against the stigma. But the 
strongest indication of the existence of a species of 
sensitive principle in a plant is, perhaps, that ex¬ 
hibited by the Desmodium gyrans. It is a native of 
India, growing on the banks of the Ganges, but may be 
seen in one of the stoves at Kew. Its leaves are ternate, 
the middle leaflet being larger than the lateral ones. 
All of them at intervals are in vibratory motion; some¬ 
times equably, at other times abruptly, but without any 
unison in the movements. If their motion be prevented, 
by grasping them in the hand, they renew it more vigor¬ 
ously when the confinement is removed, but by degrees 
subside to their natural rapidity of motion. This motion 
does not depend upon the application of any external 
stimulus, for it continues throughout the night as well 
as the day. It is most active during a warm day, the 
leaves then having an additional tremulous motion. 
If other evidence be required, let us remember that 
some plants close their flowers invariably when rain is 
approaching. Others have an unalterable direction as¬ 
sumed by them when climbing. No force can make one 
twist round a pole from left to right, if its natural direc¬ 
tion be from right to left. If a garden pot be divided 
by a vertical partition, and one half filled with a poor 
sterile earth, and the other moiety with a rich fertile 
soil, a geranium or other plant placed in this pot, with 
some of its roots over the sterile soil, and the rest of 
the roots over tlio fertile soil, those over the first 
named portion will gradually change their direction 
until they can also get into the richer pasturage. In¬ 
stances have been known of the roots of trees piercing 
and destroying walls in their efforts to attain a more pre¬ 
ferable soil than that in which they were planted. M. 
Saussure relates that he placed some plants of Poly¬ 
gonum persicana and Bidens cannabina in water con¬ 
taining acetate of lime in solution. These plants then 
imbibed, with the water, a portion of this salt; but 
when they had the opportunity of selection given them, 
by dissolving in the water some common salt, glauber 
THE COTTAGE GARDENER. 
