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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



each other? The results of these experiments show that no 

 ray, or indeed any limited group of rays, are sufficient per se, in- 

 asmuch as growth under each of the coloured glasses falls far 

 short of that of plants when growing normally in open ground. 



Again, on ascertaining the amounts per cent, of water, as well 

 as of dry substance, in each case, the results are very different. 

 Thus, e.g., the effects of red and yellow are alike (Table IV. 

 col. 4), while that of blue approximates that of clear glass. 



Hence the results show that any single curve drawn to 

 indicate the assimilative powers of chlorophyll corresponding 

 with the several rays of the solar spectrum will be insufficient ; 

 for it is quite as important to observe the relative amounts of 

 dry substance formed as it is to note the absolute amount of 

 growth, as indicated by the total weights. 



The general result arrived at by a study of the different 

 effects of each colour is that every ray requires tlie aid of all 

 the others for effective growth. 



The fact appears to be that green plants are naturally 

 attuned to receive the vibrations of all kinds of rays, of course 

 within prescribed limits of intensity, including those of a proper 

 temperature ; so that every phase of their energies becomes at 

 once impeded if the luminous environment be deficient in any 

 one or more particulars, though all the rays of the spectrum are 

 required for perfect functions. We see that certain rays when 

 in excess will stimulate the effect due to that particular part of 

 the spectrum. Thus under red and yellow we find the stimulus 

 of heat to be in excess, and so its effects become injurious. 

 Under blue, however, several observers think that they have 

 discovered a stimulus to activities, engendering a precocity of 

 growth especially perhaps in germination. Thus Mr. Hunt, in a 

 paper read before the British Association in 1845, described a 

 process which consisted in covering germinating seeds with glass 

 coloured blue by cobalt. That author also read a letter from 

 the Messrs. Lawson, in which they stated that by allowing seeds 

 to germinate under blue glass they had succeeded in raising a 

 larger number of seeds in a given time as well as producing 

 germination in a shorter period.* This has been corroborated 

 by M. Berl ; and a London florist has described to me his method 

 of hastening the flowering of the Lily -of-thc- Valley by subjecting 

 * Gardener^ Chronicle, 1853, p. 601. 



