479 
Wager . — The Perception of Light in Plants. 
Schistostega osmundacea. The protonema of this moss, which is found 
in caves, is luminous. The cells are shaped like a convex lens above, and 
the chlorophyll grains are found in the basal part of the cells, which is 
conical. The rays of light which fall upon the cell are refracted and concen- 
trated upon the chlorophyll grains. Owing to the shape of the cell, some of 
the rays are totally internally reflected from the basal walls of the cell and 
are again emitted, which gives the luminous appearance. Noll showed also 
that a variation in the direction of the light rays was accompanied by 
a corresponding movement of the chlorophyll grains, in order that they 
might always be in a position to take the fullest advantage of the concen- 
tration of the light. 
The arrangement of the chlorophyll grains in such plants as Oxalis 
acetosella , various species of Begonia , and other shade plants favours this 
view. Schiirhoff 1 has also shown that in some species of Peperomia the upper 
convex walls of the palisade cells, together with the contained calcium 
oxalate crystal, act as lenses for the concentration of light on the chloro- 
phyll grains, as well as for light perception. 
In Botrydinm granulatum the chlorophyll grains are distributed more 
or less evenly over the whole interior surface of the nearly spherical cell, the 
rest of the cell being filled with a clear cell-sap. As the plant grows 
in shady places, such as roadside ditches and damp clayey soil under trees) 
and possesses no means of orientation, a portion of the chlorophyll grains 
would be always in obscurity, if it were not that the spherical shape of the 
cell brings about a total internal reflection of some of the rays of light 
which pass into it. In this plant, however, it is not so much the condensa- 
tion of the light as the more efficient distribution of it that is important. 
In leaves with more or less elongate palisade cells, it is also probable 
that the direct condensation of the rays of light upon the chlorophyll grains 
is not so important as the more efficient dispersal of them among the 
chlorophyll grains, due to their being brought to a focus in the palisade 
cells, instead of passing straight through them, as would be the case if 
no convergence were possible, as in leaves with flat outer w r alls. 
In those shade plants, and in the species of Peperomia cited by Stahl 
(loc. cit.), where the rays of light are brought to a focus above (in front of) the 
cup-shaped or short palisade cells, we should also have, not a condensation 
of the light rays, but a more efficient distribution of them over the chloro- 
phyll grains, due to their divergence after passing the focal point. This 
would be the greater owing to the number of different focal points produced, 
a consequence of the spherical aberration due to the conical shape of 
the cell. 
aus dem botanischen Institut zu Wurzburg, iii, 1887. See also W. West, Luminosity of Schistostega 
osmundacea . Naturalist, 256, 1907. 
1 Ozellen undLichtkondensoren bei einigen Peperomien. Beil. z. bot. Centralbl., xxiii, p. 14, 1908. 
