338 
THE LADIES’ MAGAZINE OF GARDENING. 
it still remains colourless; hut, if this salt be decomposed by electrical 
agency, then the acid and alkaline ingredients, being separated, at once 
produce their red and green colours. Now, if we suppose the carbonic 
acid gas, which enters the parenchyme of the leaves, to be attracted by, 
and to combine with, the alkaline matter which is so abundant in those 
organs, it may there form a neutral salt, and whilst this neutral state 
continues the leaf will remain colourless ; but if the chemical rays of 
light, acting like electricity in the example before given, decompose this 
carbonate, and cause the expulsion of its acid ingredient, then the alkali, 
becoming predominant, will produce its usual effect on the xanthogen of 
the leaf, and its chromule will in consequence be rendered green. In order 
to maintain this green colour in the leaf, the action of light on its saline 
ingredients must be regarded as in continual operation; and hence its 
exclusion, by suspending that action, is followed by a gradual loss of 
colour; and, as the carbonic acid gas is no longer decomposed, the leaf at 
the same time ceases to afford oxygen gas. The colouration of the 
leaf, therefore, is not immediately due to the evolution of oxygen, nor 
even to the subtraction of carbonic acid, but to the predominance of 
alkaline matter which that subtraction of acids occasions; consequently, 
the verdure succeeds to the decomposition of the acid, the evidence of 
which is afforded by the expulsion of oxygen gas. Hence, to speak 
correctly, we cannot so properly say that the green leaf affords oxygen, as 
that it becomes green when that gas is expelled ; and thus it is, that the 
decomposition of carbonic acid by the agency of light gives rise, at once, 
to the evolution of oxygen gas, and the formation of the green colour in 
plants. 
Conclusion .*—We cannot close our remarks without congratulating 
Mr. Ward on the occurrence of the fortunate incident which first sug¬ 
gested his inquiries, and on the zeal and perseverance displayed in the 
experiments which ultimately terminated in the construction of the appa¬ 
ratus which has so long engaged our attention. To himself success must 
be peculiarly gratifying, inasmuch as it enables him to indulge his taste 
in the pursuit of a favourite science, which the locality of his residence 
otherwise forbade him to cultivate. 
It is a great advantage of his method that it may now be put in prac¬ 
tice by others, as it was at first by himself, simply by confining a single 
plant in a bottle, as well as by enclosing a greater number in the more 
costly apparatus which has just been described. It may, therefore, be 
practised to any extent, or adapted to any scale of expense, which the 
individual may find it either convenient or desirable to employ. When 
once fitted up, the apparatus, be it either small or large, requires scarcely 
