144 M. Marc Miclieli on some Recent 



The cause of this phenomenon has exercised the sagacity of 

 physiologists ; and it has finally been recognized that this 

 change of colour was only apparent, and that it resulted from 

 certain movements performed by the granules of chlorophyl 

 in the interior of the cell. 



The first observation of this kind is due to M. Famintzin*, 

 author of numerous investigations upon liglit and vegetation. 

 He observed that in the leaves of certain mosses {Mmum, sp.) 

 the granules of chlorophyl group themselves during the day 

 in the cells along the horizontal walls or those parallel to the 

 surface. During the night they execute a movement of re- 

 treat and place themselves along the walls perpendicular to 

 the surface. This phenomenon is exclusively due to the in- 

 fluence of light ; heat has nothing to do with it. 



Of the different rays the most refrangible alone have the 

 faculty of drawing the chlorophyl towards the surface. The 

 most luminous rays produce the same effect as complete 

 darkness. 



These results being once known, the same subject was taken 

 up and treated more profoundly by M. Borodin f. He studied a 

 great number of plants, both cryptogamous and phanerogamous. 

 Among the latter he especially paid attention to those whose 

 transparent tissues rendered observation easy ( CalUtriche^ Stel- 

 laria^ Ceratophyllum, and Lemna trisidca). He recognized 

 three different phases in the phenomenon. Like M. Famintzin, 

 he saw the chlorophyl place itself along the horizontal walls 

 under the influence of light, and retire in darkness : but he 

 likewise remarked that too ardent a sun exerts the same action 

 as darkness ; under the influence of its rays the granules of 

 chlorophyl quit the horizontal walls and move towards the 

 perpendicular ones. This action fully suffices to explain the 

 changes of colour indicated by M. Sachs. In fact in diffused 

 light the chlorophyl covers the horizontal walls (or those which 

 alone strike our eyes), and the leaf thus appears darker. In 

 the open sun or in obscurity these same walls, being almost 

 completely deprived of chlorophyl, of course give us the im- 

 pression of a lighter tint. 



With regard to the effect of the different regions of the 

 spectrum, M. Borodin perfectly agrees with his predecessor. 



Researches of the same kind have also been made by M. 

 PrilleuxJ upon the leaves of a moss [Funaria hygrometrica) . 



* Pringsheim's Jahrb. fiir wisa. Botanik, Bd. v. p. 49. 

 t Melanges Biologiques tires du Bull, de I'Acad. Imp. de St. P^tersb. 

 tome vii. (1869) p. 50 ; and Bot. Zeit. 1869, No. 38. 

 X Comptes Rendus, 1870, tome Ixx. 



