258 
PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
the agitation of the wind. A great number of floating plants of Lenina were success- 
ively placed in the dark part of the vessel. Though they could freely move on the 
water by the smallest impulse, 1 never saw them come near the lighted part or move 
into it, even when the experiment was continued long enough to allow the symptoms 
of blanching, already mentioned, to manifest themselves in the Lemnse. No motion 
towards the light was ever perceived. It is to be understood that, for such a result, 
it is necessary that there should not be any possibility of shaking or vibration in the 
liquid, and a first experiment, undertaken without sufficient precautions in that 
respect, gave results by which I was at first deceived. My doubts on this result 
were excited by the following experiment. In a tumbler completely covered with 
thick black paper, I put some water on which I placed a few floating plants of Lemna. 
A narrow slip was cut out in the paper on the side opposite to the light, so as to 
bring a single ray across the vessel. The apparatus, covered over with a thick book, 
was left in a place not exposed to vibration. The Leranas did not change the position 
which they had been placed in, and, far from arranging themselves, as I expected, 
in a line along the luminous ray, they did not move at all towards the illuminated 
space. Varied in different ways, the experiments with the Lemnas have always 
given negative results to the supposition that they have a real attraction exercised on 
them by light. 
I have endeavoured to repeat the experiments on other plants. I have ascertained 
that seeds of peas, French beans, mustard, &c. put on floating pieces of cork in a 
vessel filled with water, not only did germinate, but that the plant produced could 
develope itself without any other care than replacing the evaporated or absorbed 
water. It could thus furnish a complete vegetative course, expand its leaves, make 
its flowers blow, and even bring its fruit to maturity ; only the stems are very slender 
and the leaves smaller than usual. 
The germination of seeds took place pretty nearly in the same way, whether they 
were exposed to light or kept in complete obscurity. As it had been said that light 
exercises an influence on the direction of roots, I made an experiment with four peas, 
placed on floating pieces of cork. The first (No. 1) was left to germinate and grew 
in a common glass tumbler; the second (No. 2) in a tumbler covered with black 
paper, but leaving a thin stream of light to enter by a slit in the paper ; the third 
(No. 3) in a glass coloured blue, and admitting only a thin stream of blue light ; and 
the last (No. 4) was kept in complete obscurity. The seed in the free light developed 
itself well, and in twenty-four days exhibited a strong stem of a fine green colour, 
five inches long and well-stocked with leaves. Nothing remarkable occurred in the 
roots. 
No. 2, receiving only a ray of common light, germinated well and reached its full 
growth. After eighteen days its stem was four and a half inches in length. The root 
was very long, six inches at least, and was covered with small branching roots, which 
had all been formed on the side of the opening that admitted light, and had directed 
