\/A' \V 1 1 1.1 AM .S7/-..I//-;.V.S, J-.K.S. 255 



showed signs of destruction when exposed to the naked electric 

 light, and these destructive influences were perceptible, though 

 in a less marked degree, at a distance of 20 feet from the source 

 of light. 



A question here presents itself that can hardly fail to excite the 

 iiu crest of the physiological botanist. The clear glass does not 

 upparently intercept any of the luminous rays, which cannot 

 therefore be the cause of the destructive action. Professor Stokes 

 has shown, however, in 1853, that the electric arc is particularly 

 rich in highly refrangible invisible rays, and that these are largely 

 absorbed iu their passage through clear glass, it therefore appears 

 reasonable to suppose that it is those highly refrangible rays 

 beyond the visible spectrum that work destruction on vegetable 

 cells, thus contrasting with the luminous rays of less refrangibility, 

 which, on the contrary, stimulate their organic action. 



Being desirous to follow up this inquiry a little further, I sowed 

 a portion of the ground in the experimental conservatory with 

 mustard and other quick-growing seeds, and divided the field into 

 equal radial portions by means of a framework, excluding diffused 

 light, but admitting light at equal distances from the electric arc. 

 The first section was under the action of the naked light, the 

 second was covered with a pane of clear glass, the third with 

 yellow glass, the fourth with red, and the fifth with blue glass. 

 The relative progress of the plants was noted from day to day, 

 and the differences of effect upon the development of the plants 

 were sufficiently striking to justify the following conclusions : 

 Under the clear glass the largest amount of and most vigorous 

 growth was induced ; the yellow glass came next in order, but the 

 plants, though nearly equal in size, were greatly inferior in colour 

 and thickness of stem to those under the clear glass ; the red glass 

 gives rise to lanky growth and yellowish leaf; while the blue glass 

 produces still more lanky growth and sickly leaf. The uncovered 

 compartment showed a stunted growth, with a very dark and 

 partly shrivelled leaf. It should be observed that the electric 

 light was kept on from f> P.M. till G A.M. every night except 

 Sundays during the experiment, which took place in January, 

 1881, but that diffused daylight was not excluded during the 

 intervals ; also that circulation of air through the dividing frame- 

 work was provided for. 



