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- 
