272 Mr. Hunto;i Ltight *which has permeated coloured Media, 
the cuticle in the blue and green lights, before any change 
was evident in the other parts. 
After ten days, under the blue fluid there was a crop of 
cress, of as bright a green as any which grew in full light, and 
Jar more abundant. 
The crop was scanty under the green fluid and of a pale 
unhealthy colour (15.). 
Under the yellow solution but two or three plants appeared, 
yet they were less pale than those which had grown in green 
light. Beneath the red bottle the number of plants which 
grew was also small, although rather more than in the spot 
the yellow covered. They too were of an unhealthy colour. 
17. I now reversed the order of the bottles, fixing the 
red in the place of the blue, and the yellow in that of the 
green. After a few days’ exposure the healthy cress appeared 
blighted, while a few more unhealthy plants began to show 
themselves, from the influence of the blue rays, in the spot 
originally subjected to the red. 
It is evident from this that the red and yellow rays not 
merely retard germination, but positively destroy the vital 
principle in the seed. Prolonged exposure uncovered, with 
genial warmth, free air, and indeed all that can induce growth, 
fails to revive the blighted vegetation. 
I have repeated the experiment many times, varying the 
fluids, but the results have been the same. At this time I have 
the above facts strikingly exemplified where the space co- 
vered by the bichromate of potassa is without a plant. 
These results merit the attention of those who are engaged 
in the study of vegetable oeconomy. Do they not point at a 
process by which the productions of climes more redolent of 
light than ours may be brought in this island to their native 
perfection ? 
Dr. Draper’s ‘‘ experiments” (Philosophical Magazine, 
Feb. 1840, pres. vol. p. 81) appear at variance with mine. 
Under the influence of a nearly tropical sun permeating 
half an inch of solution of the bichromate of potassa, cress 
grew of a green colour, whilst it took five days to give a sen- 
sitive paper a faint yellow green colour. From this Professor 
Draper argues the existence of two classes of rays, a different 
class being necessary to produce the green colouring of vege- 
table foliage from that which darkens chloride of silver. 
With submission to one whose facilities for such inquiries 
are so much greater than my own, I would suggest a repe- 
tition of the experiments with some of the recently discovered 
photographic preparations. The papers f and h, both under 
