Application of the Micro-spectroscope, &c. By Thos. Palmer. 225 
of respiration, &c., the first questions which naturally arise are, 
how do they live, and what do they breathe ? This is all answered 
by the text-books of botany, but the internal portion of their exist- 
ence, and that of which we know so little at present, viz. the forma- 
tion, production, and the carrying out of a perfect system in them- 
selves, is still a mystery, and consequently need workers. But to 
begin with the way in which plants live, respire, and grow, or 
rather how the internal machinery is set up, kept in motion, for a 
distinct purpose, and thoroughly and most efficiently carried out, 
inevitably craves our first attention. 
From the experiments of De Saussure, we learn that the 
quantity of carbonic acid absorbed and decomposed by plants varies 
greatly in different species even when placed in the same circum- 
stances. Lythrum salicaria was found to absorb seven to eight 
times its bulk of this gas in a day ; while the Cactus opuntia, and 
other fleshy-leaved plants, did not absorb above a fifth of that 
quantity. The proportion absorbed, according to this author, de- 
pends upon the surface of the plant ; and therefore thin- leaved 
plants must absorb more than those that have fleshy ones. The 
whole of the oxygen contained in the carbonic acid is not absorbed, 
but is emitted again by the plant. This has been clearly shown 
to be the case by the same author’s experiments, one of which, I 
thought, might not prove out of place here. 
Carbonic acid was mixed with common air in such a proportion 
that it occupied 7 • 5 hundredths of the total mass. Jars stood 
over mercury, covered with a thin film of water, were filled with this 
mixture ; and plants of Vinca minor, growing in a small vessel of 
water, were introduced into each. These plants, thus placed, were 
exposed for six successive days to the sun, from five to eleven in the 
morning, while the temperature was at TCP, during the whole of 
which time they vegetated with great vigour. The bulk of the air 
in the jars was not altered, neither could any carbonic acid be de- 
tected in it, though the proportion of oxygen was 2fp per cent. 
The whole of the carbonic acid, amounting to 21 ‘75 inches, was 
therefore absorbed, while the oxygen emitted was only 14 '72 
inches, whereas the whole of the oxygen contained in the carbonic 
acid would have amounted to 21 '75 inches. The difference of 
about 7 inches was found to be composed principally of azote, which 
was given out by the plants in combination with the oxygen. The 
whole will be clearly seen on referring to the annexed table : 
When put in. 
When taken out. 
.. 218-95 
Azote .. 
Oxygen 
Carbonic acid 
211-92 .. 
56-33 .. 
21-75 .. 
71-05 
290-00 .. .. 290-00 
