Intelligence and Miscellaneous Articles, 485 



ON THE INFLUENCE OF VARIOUS COLOURED RAYS ON THE DE- 

 COMPOSITION OF CARBONIC ACID IN PLANTS. BY M. CAIL- 

 LETET. 



It has long been observed that the green parts of plants exposed 

 to the direct rays of the sun possess the property of decomposing 

 the carbonic acid in the air, and of disengaging an almost equivalent 

 quantity of oxygen. In darkness the converse phenomenon is pro- 

 duced : the oxygen of the air is absorbed, and carbonic acid is dis- 

 engaged, arising from the oxidation of part of the carbon of the plant. 



In the experiments I have undertaken to ascertain the influence of 

 the various coloured rays on the decomposition of carbonic acid by 

 plants, I have endeavoured to attain as far as possible the conditions 

 under which nature works. 



I had to arrange my coloured glasses so as to prevent, by a consi- 

 derable draught of air, the great increase of temperature produced 

 in closed vessels exposed to the direct solar rays. Under a red glass 

 I have observed the temperature rise to above 70°. 



By preliminary trials I found that by taking some precautions the 

 detached leaves acted on mixtures of gases as if they still adhered to 

 the plant which produced them. I have also found that leaves of 

 the same plant and of equal surfaces virtually decompose the same 

 quantities of carbonic acid when they act upon the same gaseous 

 mixtures exposed to the same source of light. 



The absorption of carbonic acid, and the disengagement of oxygen 

 more or less mixed with nitrogen, is met with exclusively in the 

 green parts of vegetables ; but it is indispensable that the organs 

 be intact, for by crushing or even by rubbing them the property of 

 absorption is destroyed. When a leaf is carefully cut into small 

 fragments the decomposing action is still manifest ; for each part, 

 containing all the anatomical elements, acts like an entire leaf. A 

 temperature of 10° to 15° C. is necessary for the manifestation of the 

 decomposing action, but the rays of obscure heat are insufficient to 

 produce it. This I have been able to ascertain by means of an ap- 

 paratus which I owe to the skill of M. M. Alvergniat. 



It consists of two concentric gas-jars of colourless glass sealed at 

 the bottom. In the space between these two vessels of different 

 diameter there is a concentrated solution of iodine in bisulphide of 

 carbon. This screen only allows obscure heat to traverse it ; and it 

 can be ascertained that carbonic acid placed in the central gas-jar is 

 not decomposed by the leaves, spite of the continued action of the 

 sun's rays. 



The different coloured rays have, on the contrary, a special action 

 more or less energetic in the decomposition of carbonic acid. When 

 tubes containing leaves of the same plant equal in surface are placed 

 in the same gaseous mixture under bell-jars of different colours, after 

 eight or ten hours' exposure to the sun, the quantities of carbonic 

 acid left undecomposed are stated in the following Table. 



