18 
QTJINOLOGY OF THE EAST INDIAN PLANTATIONS. 
of all parts in which they are found to the vivifying action of the air they convey.* This is compared to the 
manner in which insects are supplied with air through the trachea which pervade their bodies. It has hence 
been called the trachean respiration .t 
The general result is that the sap experiences modifications which change its nature. By transpiration 
it loses a portion of the water of which it was composed ; by varied secretions it throws off certain products 
useless or foreign to its nutrition; and by its contact with atmospheric air — that is, its respiration — it 
acquires new properties, being converted into a fluid which descends from the leaves towards the roots, 
constituting what has been called the descending or, more properly still, the nourishing sap,% which seems to 
he attracted towards any part of the plant where special need exists for its services, as in the case we are 
here considering of the renewal of the bark after decortication. 
As I have chiefly to treat of this kind of respiration which appears to be constantly going forward, 
though it has sometimes been named nocturnal respiration , and which supplies oxygen to the plant, I shall 
adopt for it the more correct term of general respiration ; § in opposition to that peculiar respiration of the 
leaves and other green portions of the plant, by virtue of which, under the influence of sunlight, the carbonic 
acid of the air is decomposed, carbon is fixed, oxygen is disengaged, and the growth of the plant ensured. 
This latter has been named the chlorophy Ilian respiration , and on it all vegetable organization seems 
primarily to depend. Leaves, when once thoroughly exsiccated, lose the power of decomposing carbonic 
acid, and no restoration of water will renew this action. || The leaf, thus dried, dies, because it ceases to 
breathe ; it is possible to kill it by suspending its respiration (by means of an artificial atmosphere of azote 
or some other gases) for a sufficient time, and that without the cells being injured, without elimination of 
the water essential to its organization, without any perceptible modification of the green colouring-matter. 
This is the asphyxia of leaves.^] 
Researches of M. Decaisne. 
In connection with these researches I heard of a work of M. J. Decaisne** on Madder which at once 
engaged my attention, as having myself studied the red colouring-matter of this plant, whilst occupied more 
particularly with that of the C. succirubra. I found, as I expected, considerable analogy, though not 
identity, between the two, as was to be looked for in plants so nearly allied botanically. I did not then 
pursue the subject : but when I read M. Decaisne’s elaborate and very complete treatise, I was charmed not 
only with the clear and lucid style which, in common with his compatriots, he knows how to apply to scien- 
tific subjects, but also with the details of the investigation ; throwing, as it seems to me, much light on the 
question, and, though published many years ago, not equalled, to my knowledge, by anything that has since 
been given to the public. He says, in the commencement of his preface, that he considered many of the 
principal facts and phenomena which he had to study might be explained by the knowledge acquired 
respecting the respiration of vegetables, and consequently the facts thus established became the point of 
departure of his experiments. The theory of the coloration of plants is dependent on the knowledge 
of the functions of the leaves, which are themselves pretty generally the seat of this coloration ; and as the 
action of light exercises great influence on the respiration, which again is ultimately connected with the 
phenomena of the immediate principles of vegetables, he thought it was needful to study the action on the 
m 
* A. Richard, ‘Nouveaux Elements de Botanique/ Pans, 1864, p. 152. 
f M. Dutrochet ascertained by experiment that the air contained in the different parts of the plant underwent a change 
proportion to its distance from the orifices in the leaves, through which it must enter ; as it circulates in the pneumatic vessels it 
loses a portion of its oxygen, which is absorbed by the sap in proportion as it traverses the vegetable tissue. (A. Richard, 
ut supra, p. 157.) Thus the air contained in the stem of the water-lily showed only sixteen parts of oxygen in a hundred, and that 
in the roots, only eight in a hundred. 
% Duchartre, 'Elements/ p. 716. § Duchartre, ut supra, p. 751. 
|| Boussingault, " Etude sur les fonctions des feuilles ” (Ann. de Chimie et de Physique, mars 1868, p. 333). 
*' LI. p. 339. ** ‘ Recherches anatomiques et physiologiques sur la Garance/ 
