LIGHT AND LIFE. HI 



Flowers, fruits, and leaves, then, are elaborated by the 

 help of luminous vibrations. Their tissue holds the sun's 

 rays. Those charming colors, those fragrant perfumes, and 

 delicious flavors, all the innocent pleasures the vegetable 

 kingdom yields us, owe their creation to light. The subtile 

 working of these wonderful operations eludes us, as does 

 that which guides the fleeting diffusion and thousand-fold 

 refractions displayed by the imposing spectacle of the 

 dawn ; but is it nothing to gain a glimpse of those primal 

 laws, and to possess even a twilight ray upon these mag- 

 nificent phenomena ? 



n. 



Light exerts a mechanical influence on vegetables. The 

 sleep of flowers, the bending of their stems, the nutation 

 of heliotropic plants, the inter-cellular movements of chlo- 

 rophyll, offer proofs of an extremely delicate sensitiveness 

 of certain plants in this respect. Pliny mentions the plant 

 called the sunflower, which always looks toward the sun, 

 and steadily follows its motion. He notices, too, that the 

 lupin always follows the sun in its daily movement, and 

 points out the hour for laborers. Tessier, at the end of 

 the last century, took up the ' study of these phenomena, 

 and inferred in a general way that the stems of plants al- 

 ways turn toward the light, and bend over, if necessary, to 

 receive it. He noted, too, that leaves tend to turn toward 

 the side whence daylight comes. Payer made more exact 

 experiments. He tried them with young stems of common 

 garden cresses grown on damp cotton in the dark. These 

 stems have the property of curving and turning quickly 

 when placed in a room lighted only from one side or in a 

 box receiving light on one wall only. The upper part of 

 the stem curves first, the lower part remaining straight. 

 By a second movement the top erects and the bottom bends 

 over, so that the plant, though leaning, becomes almost 



