50i> Plant Case for growing Plants 



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 coloration 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 acid 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 

 suggested his enquiries, and on the zeal and perseverance dis- 

 played in the experiments which ultimately terminated in the 

 construction of the apparatus 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 practice 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 any farther care or attendance. No fresh watering or 

 airing is at any time required ; nor is any inconvenience ex- 

 perienced from dust and litter, which often render the ordinary 

 mode of keeping plants in well-furnished apartments objection- 

 able and troublesome. Farther, as the plants in this apparatus 

 are shut off from all communication with the external air, no 

 apprehension of their injuring the atmosphere, even of close 

 rooms, can be reasonably entertained. The only condition, in 

 regard to attendance, that claims observance, is an occasional 

 exposure to light, perhaps for a short period only on days of 



