CHEMICAL AND MICROSCOPICAL INVESTIGATIONS. 
21 
the bark, especially when old and weathered; that it is the original yellowish mother-substance found in 
the heart-wood which turns pink or brick-red in the bark, under the influence of the oxygen of the air, 
especially when assisted by the presence of earth and alkalies, and that the various products, including 
perhaps the alkaloid, are derived or rather built up from this under the influence of the respiration of the 
plant. By the respiration of the plant, in this instance, I mean specially the general respiration, in 
opposition to the chlorophyllian respiration. The object of this latter is to fix carbon for the development 
of the plant, and is, of course, quite essential to its vigour and even to its existence; but I have long- 
suspected that the development of the alkaloids and of Quinine, more particularly, did not stand in any 
special relation to the vigour of the plant ; that in fact, where this was impeded, as in very great elevations, 
where more especially the plant had to clothe itself with much cellular tissue, there was Quinine the most 
abundant ; the explanation being that the cellular tissue is the place of deposit for the peculiar products of 
the plant, as I have shown in my examination of the internal and external bark. I now proceed to notice 
one more fact connected with M. Decaisne’s researches on madder, which seems to have analogy with the 
point I am considering. It appears that the cultivators of madder were in the habit of covering up with 
earth those portions of the stalk of the plant in which they wished to develope the peculiar colouring-matter 
in place of the chlorophyll, in order to add these etiolated stalks to the roots, in which alone the colouring- 
matter is found to perfection. M. Decaisne observed,* in examining microscopically the cellular tissue, that 
the cells of the root secrete a yellow liquid, whilst those of the stalk, which are to all appearance identical, 
become filled with green colouring-matter ; and he proposed to himself this question, “ Is this so great 
difference in the secretions, the invariable result of the tissue of the roots, as is the case in certain plants, 
or does the influence of external agents contribute to reproduce this phenomenon on other parts of the 
vegetable?” Well-devised experiments showed that it is possible to change at discretion the produc- 
tion of chlorophyll into the elaboration of colouring-matter similar to that of the roots. It happens in 
this case that the green portions which, when exposed to light, absorb the carbonic acid of the air 
whilst disengaging oxygen, thus augmenting the quantity of carbon which the plant contains, absorb, on the 
contrary, in darkness, a part of the oxygen of the atmosphere which surrounds them and replace it with 
carbonic acid. 
This singularly interesting investigation may perhaps throw some light on the manner in which Mr. 
MTvor is able — apparently by causing the general to take the place of the chlorophyllian respiration — to 
cause the plants to produce alkaloids of a better quality, and more easily purified from green and other 
colouring-matters. It suggests the question, Whether the plant may not really produce alkaloid instead of 
chlorophyll? It is by shrouding the bark of the plant in darkness and moisture that the madder is com- 
pelled to produce red colouring-matter instead of chlorophyll. It is by a like process that the Bed-bark - 
tree is made to produce a richer and better bark in the process of MTvor. 
These facts suggest the idea that in connection with the above change in the respiration, under the 
influence of the presence or the withdrawal of light, there may be a change in the electrical state, and 
hence in the chemical activities of the cells themselves, so that the same cells, which under one set of 
conditions produce one result, under the stimulus of the ray of light, may produce other combinations. 
M. Cailletet remarks in a recent papert that, “ the calorific rays, as well as the chemical rays, are 
without action on the strange decomposition of carbonic acid by vegetables, which takes place under 
conditions altogether different from those which we know howto produce in our laboratories; but the 
forces which determine this decomposition act upon the elements of this compound body dissolved in the 
liquids of the leaf, and we must confess our entire ignorance of the state these elements are in when in 
* f Recberclies/ p. 22. 
t “De Tinfliience des divers rayons colores sur la decomposition de Pacide carbonique par les plantes/' par M. L. Cailletet 
(‘ Journal de Pharmacie et de Chimie/ Oct. 1867). 
G 
