ON THE INPLUKNCE OP LIGHT ON THE GROWTH OP PLANTS. 31 



grown under the influence of the yellow had white stalks, all the lower leaves 

 were of a very delicate green, whilst the upper ones were yellow. An open- 

 ing in the upper cover of the box admitted a little white light from the 

 northern sky, and under its influence the leaves above the yellow ones became 

 green. These specimens were carefully dried in the sunshine, by which they 

 lost in weight respectively as follows : — 



Those grown under the blue media 178'9 grs. or 91"4 per cent. 

 Those grown under the red media 252-2 grs. or 91 '3 per cent. 

 Those grown under the green media 219'4 grs. or 90" 1 per cent. 

 Those grown under the yellow media 239*1 grs. or 90-6 per cent. 



When, however, these were placed on a stove, and still higher dried, the 

 results wei'e more equalized ; 



The plants under the blue losing 92'84 per cent. 

 The plants under the red losing 92*75 per cent. 

 The plants under the green losing 92*40 per cent. 

 The plants under the yellow losing 92*31 per cent. 



From the above results it would appear that the rays which permeated the 

 green and yellow media, had the property of occasioning the secretion of 

 larger quantities of woody fibre than the other rays, the quantities of water 

 or volatile matter being greater in the plants grown under the blue and red ; 



Those under the blue leaving 7*16 per cent, of woody fibre. 

 Those under the red leaving 7*25 per cent, of woody fibre. 

 Those under the green leaving 7*60 per cent, of woody fibre. 

 Those under the yellow leaving 7*69 per cent, of woody fibre. 



These facts certainly appear to strengthen the opinion which has been ex- 

 pressed by Dr. Daubeny and others, that the decomposition of carbonic acid 

 in plants is eflected by the yellow or luminous ray. I have on two previous 

 occasions stated the blue rays of the spectrum to be the most active in effect- 

 ing this decomposition, and in all my experiments made with a particular 

 view to the examination of this question, I have found the liberation of oxygen 

 more abundant in tubes which were placed at the blue end of the spectrum ; 

 these tubes being filled with water holding carbonic acid in solution, and 

 some small leaves plucked from my garden. I have only stated the results of 

 one set of my experiments in which the balance was used to test them. It 

 is due to those holding a different view from myself, to state that three sets 

 of experiments gave nearly similar results. At the same time, as these expe- 

 riments would appear to show that yellow light is not injurious to the growth 

 of young plants, it must be most distinctly understood that the contrary has 

 been, in every instance, proved to be the case. The plants have always been 

 more or less etiolated, whereas those which have grown under the influence 

 of the blue rays, have always presented lively and beautifully green leaves. I 

 cannot, therefore, admit at present that the formation of chlorophylle is due to 

 the luminous rays. 



April ] 9th. — Seeds of the sweet-scented-pea and mignonette were planted 

 in the partitions of boxes, arranged as above. On the 29th the seeds under 

 the blue and red media had thrown up leaves in abundance ; those under the 

 blue being marked by their very healthful character. A few dwarfed and 

 miserably pale plants had appeared under the green media, but not one under 

 the yellow media. After a few days the peas under the yellow began to 

 germinate, and the plants presented tlie same aspect as I have described. 

 But although the most careful attention was given I could not succeed in 



