112 NATURE AND LIFE. 



rectilinear again. When put in a room receiving light 

 from two windows, the following results are noticed : If 

 the openings are on the same side admitting light equally, 

 the stem bends in the direction of the middle of the angle 

 formed by these two beams ; if one of the two windows 

 admits more light than the other, the stem leans toward it ; 

 if the windows are opposite each other, the stem stands 

 erect, when light comes equally from both sides, and, if it 

 does not, turns toward the stronger rays. Payer discovered, 

 moreover, that the part of the irradiating light most active 

 in its effects corresponds in this case to the violet and the 

 blue. The red, orange, yellow, and green rays do not 

 seem to produce any movement in plants. Gardner car- 

 ried the investigation still further. He sowed turnips, and 

 let them develop in the dark to two or three inches in 

 length. Then he threw the solar spectrum by a prism on 

 this little field. The plants inclined toward a common 

 axis. Those exposed to the red, orange, yellow, and green 

 rays, leaned toward the deep blue, while the part lighted 

 by violet bent in the opposite direction. Thus the crop 

 took the appearance of a wheat-field bowing under two 

 contrary winds. The turnips placed in the violet-blue 

 region looked toward the prism. Gardner thus determined, 

 as Payer had done, that the most refrangible rays are those 

 which effect the bending of the young stems. He proved 

 also that the plants grow erect again in the dark. 



These experiments, repeated and varied in many ways 

 by Dutrochet and Guillemin, uniformly gave like results, 

 but the phenomenon itself still remains almost unexplained. 

 This remark also applies to the very singular facts of the 

 twisting of running plants. The stems of these plants, in 

 twining about their supports, usually curl from the left to 

 the right. Others follow the contrary course, and some 

 twist indifferently in either way. Charles Darwin inferred, 

 from his investigation, that light has an effect on this phe- 



