148 M. Marc Micheli on some Recent 



He operated with a solution of ammoniacal sulphate of 

 copper, not too much concentrated, and exposed his apparatus 

 to the full light of the sun or to the focus of a powerful lens 

 illuminated by a strong petroleum lamp. 



M. Baranetzky* has resumed this subject, finding that M. 

 Prilleux had operated upon very thin layers of liquid, which 

 allowed too many rays to pass, this naturally invalidating his 

 results. He employed ammoniacal oxide of copper and pro- 

 tochloride of iron, which, in layers of 25 millims. thickness, 

 divided the spectrum pretty accurately into two more and less 

 refrangible halves, but each endowed with nearly the same 

 illuminating-power. The results were exactly the same ; 

 with an equality of luminous intensity, the numbar of bubbles 

 of oxygen evolved during the act of assimilation was the 

 same. This applies also to the greening of etiolated chloro- 

 phyl, and to the destruction of the colouring principle in an 

 alcoholic solution of chlorophyl under the influence of the 

 luminous rays. Heliotropic curvatures alone evade this law, 

 and are manifested only under the influence of the blue or 

 neighbouring rays. 



The following is the mode in which, in the present state of 

 our knowledge, M. Baranetzky proposes to describe the action 

 of light : — 



a. The decomposition of carbonic acid or assimilation, the 

 formation of chlorophyl, and the destruction of the colouring 

 principle are phenomena solely dependent on the degree of 

 luminous intensity. 



h. Heliotropic curvatures, the periodical movements of 

 organs, the currents of protoplasm, and the changes of place 

 of the grains of chlorophyl are executed only under the in- 

 fluence of the most refrangible rays. 



On the decomposition of carbonic acid in the leaves, Dr. 

 PfefFer has published a workf which is perhaps the most 

 complete that we possess on this subject. From the perfec- 

 tion of the methods employed, and the care with which the 

 experiments were conducted, this work will always continue 

 to be of very great value. The conclusions, although not so 

 clear and precise as those of MM. Prilleux and Baranetzky, 

 are nevertheless in the same direction, and tend to give the 

 preponderance to the illuminating-power in the direct action 

 of the luminous rays. He expresses them in the following 

 terms : — 



" The rays of the spectrum perceptible to our eyes are the 



* Botau, Zeitung, 1871, No. 13. 



t Arbeiten des Botanischen Instituts in Wiirzburg, Oahier i.^ 1871. 



