489 
Wager . — The Perception of Light in Plants. 
Fig. 5. Rays of light brought to a focus through the granules of mucilage shown in Fig. 4. 
These granules interfere with the passage of light through the cells as a whole, and render the image 
more or less indistinct, as shown in Fig. 3. 
Fig. 6. A geometrical figure with coloured segments photographed through the cells of 
Tradescantia Jluminensis on an ortho- chromatic plate. 
Fig. 7. Saxifraga Geum. Cells of upper epidermis, showing more or less central disks of light 
thrown on to the basal walls by the minute papillae which occur in the middle of the outer cell-walls. 
Fig. 8. Shows the same disks of light moved laterally when the light is oblique. 
Fig. 9. Shows the extreme lateral movement of which they are capable when the rays which 
fall upon the leaf are still more oblique. 
Fig. 10. Upper epidermal cells of Primus lauro-cerasus. The photograph shows the illumina- 
tion of the basal walls by light which has passed through a small diaphragm T V' in diameter. 
There is no differential illumination of the basal wall. The outer walls of the cells are flat, the 
inner walls slightly curved. In spite of this absence of differential illumination, the leaves undergo 
a definite orientation into the position of equilibrium as regards the light. 
Fig. 11. Aspidistra lurida. Upper epidermal cells showing images of a six-sided figure 
photographed through the transparent nuclei. 
Fig. 12. Zebrina pendula. Image of a cabinet photograph, taken through the papillate 
projection on the outer cell-wall, and focused very nearly on the basal wall in each cell. 
PLATE XXXII. 
Fig. 13. Tradescantia Jluminensis. Basal walls of epidermal cells showing that convergence of 
light produces no differential illumination. 
Fig. 14. The same preparation. Light focused slightly below the basal walls after passing 
through a small diaphragm opening. 
Fig. 15. The same preparation, under same conditions, but focused at some distance below the 
basal walls. At this level there is a distinct differential illumination as shown by the separate 
irregular disks of light. 
Fig. 16. Basal walls of the cells in the same preparation when light falls obliquely upon the 
outer walls. Half of each basal wall is in the light and half in darkness. 
Fig. 17. Upper epidermis oi E rant his hyemalis. Shows the irregular light areas below the 
basal walls of the epidermal cells when allowed to fall upon the outer curved walls through a small 
diaphragm opening. Here and there in these light areas in each cell are to be observed clearer 
circular disks of light, due to more pronounced curvature of the cells. Each one of these is capable 
of forming an image of an object near it. 
Fig. 18. Basal walls of papillate epidermal cells of the petals of Phlox showing a clear disk of 
light in the centre of each cell. 
Fig. 19. Elongate cells of epidermis of Tradescantia virginica showing lines of light brought to 
a focus on the basal walls. The guard cells of the stomata also bring about a convergence. 
Fig. 20. Elongate cells of epidermis of Iris alata showing very bright illumination of basal 
walls when light is allowed to pass through a small diaphragm opening. 
Fig. 21. Cells of the upper epidermis of Convallaria majalis showing bands of light which are 
brought to a focus near the basal walls when a small diaphragm opening is used. 
Fig. 22. Inner epidermal cells of the sheathing leaf of Avena sativa showing the image of a 
pipe focused on or near the basal walls. At the ends of the cells, owing to a more prominent 
curvature of the outer walls, the outline of the pipe is distinctly seen, but between these there is a 
more or less continuous dark line which represents the pipe. 
Fig. 23. Epidermal cells of the leaf of Garry a elliptica showing the special lens-shaped 
thickenings of the cuticle. These are distributed more or less regularly over the whole surface of 
the leaf, independently of the position of the cells. Some of the thickenings occur exactly over the 
walls which separate neighbouring cells. 
Fig. 24. The same preparation showing the image of a cross brought to a focus near the basal 
walls of the epidermal cells. 
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