486 



Intelligence and Miscellaneous Articles. 



Rays passing 

 through 



Air mixed with CO 2 . 



Observations. 



18inl00. ! 21inl00. 



I 



30 in 100. 



Iodine dissolved in 

 bisulphide of carbon. 



Green glass 



20 



18 

 17 



7 



5 

 



21 



30 



19 

 16-5 



5-50 



1 

 



30 1 

 37 [ 



28 | 



27 



23 J 



18 

 2 



Photographic paper not 

 blackened. 



Chloride of silver slowly 

 coloured. 



Paper very rapidly black- 

 ened. 



Neither paper nor chloride 

 of silver mixed with ni- 

 trate blackened. 



Paper not blackened. 



Paper rapidly coloured. 



Violet glass 







Yellow glass 





The examination of this Table proves that the thermal rays, equally 

 with the chemical rays, are without action on the strange decomposi- 

 tion of carbonic acid by vegetables -which takes place under condi- 

 tions quite different from those we can produce in our laboratories, 

 But the forces which produce this decomposition act on the elements 

 of this compound body dissolved in the liquids of the leaf, and we 

 must avow our entire ignorance of the state in which these elements 

 exist in the solution. It would appear, from an inspection of the 

 numbers given in the Table, that the colours which are most ac- 

 tive, from the chemical point of view, are just those which least 

 favour the decomposition of carbonic acid. 



I must particularly dwell upon the special and unexpected action 

 of green light, whether this colour be obtained by a glass, by the 

 leaves of vegetables, or by coloured solutions. Under its influence, 

 carbonic acid does not seem to be decomposed at all, but, on the 

 contrary, a new quantity of the gas seems to be produced by the 

 leaves. 



For if under a green glass bell-jar, and exposed to the direct rays 

 of the sun, a gas-jar be placed containing a leaf in pure air, we 

 obtain, after the lapse of a few r hours, a quantity of carbonic acid 

 little less than would be produced by the same leaf in total 

 darkness. 



It is possibly owing to this curious property of green light, which 

 must in the long run produce the etiolation of the plants on which it 

 acts, that vegetation is generally languishing and feeble under large 

 trees, though the shade they produce is frequently not very intense. 



The results of my experiments agree with the conclusions of the 

 beautiful research published by MM. Cloez and Gratiolet on the 

 vegetation of submerged plants. Working with gaseous mixtures, I 

 have merely been able to confirm this curious property of green 

 rays, which the authors could not have been led by their special re- 

 searches to suspect. — Comjotes Ilendus, August 19, 1867. 



