PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
259 
themselves towards it, I turned the plant over so as to place the side of the large 
root deprived of small radicular threads opposite to the luminous slit. Five days 
afterwards, radicular fibrils had sprouted on that side ; and those which had developed 
themselves before, had indeed not perished, but had ceased to grow. The expe- 
riment was completed after thirty-four days. The root was then a foot long, was 
covered on all sides with radicular threads, and had turned itself into a spiral form. 
The stern was slender, very little coloured, and had a length of ten inches and 
a half. 
No. 3, receiving the blue I’ays, had, after eighteen days, a stem only three inches 
long, and the root measured four inches. The radicular threads were all on the side 
opposite to the slit giving admission to the blue light. I changed the position of the 
plant, and placed the radicular threads on the luminous side. Thirty-four days from 
the beginning of the experiment, radicular threads had sprouted on the side of the 
root where there were none before, and the root had also taken a spiral shape. It 
was seven inches long ; the stem, nine inches long, was very slender and almost white. 
No, 4, in the dark, germinated after five days, but a few radicular threads alone 
developed themselves without a stem. 
These trials were repeated on peas and mustard-seeds, and gave results of the 
same nature, as far as concerns the curling of the roots in a spiral shape under such 
circumstances, and the tendency of the white light to favour, and of the blue light 
to hinder, the growth of radicular fibrils. 
The experiments relating to the direction of the stems w'ere made pretty nearly in 
the same way as with the Lemnse ; only the vessel in which the floats were placed 
was much larger, and the diaphragm was not so near the surface of the water. 
The consequence was that the darkness of one-half of the vessel went on increasing 
from the diaphragm towards the extremity of the covered portion, and though very 
intense at that last part, was nevertheless not complete. As soon as the seeds had 
germinated, they were placed on the cork floats, in which 1 had bored a hole through 
which the root emerged into the water. The float was placed in the dark part of the 
vessel, far enough from its side to avoid the capillary attraction, and it could be moved 
by the gentlest impulse. It is hardly necessary to say that the apparatus was kept 
perfectly free from shaking or from the action of the wind. 
On the 14th of May, a pea in germination was placed on the float in the dark 
part of the vessel : it grew very slowly, and on the 22nd began to exhibit a very 
short and almost white stem. This stem by degrees became longer and longer, 
spreading itself along the surface of the water, and on the 8th of June it had reached 
the diaphragm. It formed then a long stem, etiolated, slender and white, running 
along the surface of the water ; its length was two feet. The cork float had not 
moved forwards a single line towards the luminous aperture ; only the weight of the 
plant throwing itself, as it were, all on one side, had by degrees bent down the cork 
float, but on the same spot it before occupied. When once the stem of the pea had 
MDCCCXLVIII. 2 M 
