478 
Wager . — The Perception of Light in Plants. 
The Function of the Lens Cells in the more Efficient Illumination 
of the Chlorophyll Grains. 
It is clear that the orientation of the leaf with respect to the light has 
for its main purpose the more efficient illumination of the chlorophyll 
grains ; and this must be taken into account in considering the lens function 
of the epidermal cells. Haberlandt 1 had already in 1882 suggested that 
they might bring about a more intense illumination of the chlorophyll 
grains by concentrating the light upon the chlorophyll-containing cells. 
Later, Stahl 2 showed that if sunlight is allowed to pass through the 
epidermis of a somewhat thin leaf, such as Begonia falcifolia, and observed 
through the under side by means of the microscope, the chlorophyll grains 
would be seen glistening in the bright concentrated light. Any one who 
will take the trouble to examine carefully the incidence of light upon the 
chlorophyll grains after passing through the lens-shaped epidermal cells of 
the leaves of species of Selaginella, Tradescantia jiuminensis , Adoxa mo- 
schatellina, Narcissus, Hyacinth, and many other plants will be struck 
by the very efficient illumination which is observable. As Stahl points 
out, however (loc. cit.), the concentration of the light would only be useful 
to a certain number of the assimilating cells, as there may be several under 
each epidermal cell. This is well seen in Oxalis acetosella. In species 
of Peperomia, Stahl points out, the light would be brought to a focus in the 
water-containing tissue, and not on the chlorophyll grains ; this indicates 
that the concentration must have some other purpose. He suggests that 
the papillate or dome-shaped form of the epidermal cells, which are found 
in many shade plants, may serve not so much for the concentration of the 
light as for the purpose of collecting those rays which, coming in a nearly 
parallel direction to the surface of the leaf, would be reflected from it if the 
cells were flat. The conical shape of many of the epidermal cells of shade 
plants would seem to favour this view, and Stahl shows by means of models 
that the collection of light in this way, and its utilization by the chlorophyll 
grains, is quite possible. This explanation would hardly hold good, how- 
ever, in the case of cells which possess only slightly curved outer walls. 
The numerous observations which have been made upon Schistostega 
osmundacea^ some Selaginellas, and Hepatica all clearly indicate that in 
some cases the lens cells are for the purpose of bringing about a concen- 
tration of light upon the chlorophyll grains. 
The researches of Vuillemin 3 and Noll 3 showed this very clearly in 
1 Die physiologischen Leistungen der Pflanzengewebe. Schenk’s Handbuch der Botanik, ii, 
579, 1882. 
2 Ueber bunte Laubblatter. Ann. du Jardin Bot. de Buitenzorg, xiii, 137, 1896. 
3 L’appareil reluisant du Schistostega osmundacea. Journ. de l’anatomie et de physiologic, vol. 
xxiii, p. 18, 1887; and Noll, Ueber das Leuchten von Schistostega osmundacea , Schimp. Arbeiten 
