272 Mr. Hunto?i Light ^isohich Jias 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. 1 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 ^oy^ 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. IS^O, 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 pi'oduce 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 li^ both under 



