84 Dr Gardner on the Action of Light on Vegetables. 



would, after a lengthened exposure, cause considerable deflec- 

 tion. Indeed, the phenomenon is so little dependent on the 

 brilliancy of light, that very little seems to be gained by con- 

 centrating the rays beyond a certain point. There is suificient 

 activity in each prismatic colour to produce bending, if enough 

 of time be allowed. The movement is, therefore, a result de* 

 pending upon the absorption of light. 



(23.) As this is an entirely new subject, it is thought expedi- 

 ent to advance some further evidence concerning the position of 

 the deflecting force. For this purpose the spectrum was 

 allowed to fall upon a screen, perforated by two similar aper- 

 tures, in such positions as to allow the red to pass through one, 

 and the indigo through the other. Behind the screen a box 

 was placed, containing four jars of turnip seedlings, arranged 

 along a line occupying the centre between the intromitted 

 rays. The light passed through the box without any reflexion, 

 and was stifled by black cloth when it reached the further ex- 

 tremity. All the plants commenced bending in a short time, 

 and in two hours the nearest group were inclined forwards 

 90°, and laterally 50°, towards the indigo aperture, the edges 

 of which formed the radiant. In three hours the second crop 

 exhibited the same movement ; and so with the plants of the 

 third and fourth jars. At the conclusion of the experiment, 

 in six hours and a half, all were bent forward at about 90°, 

 and each group inclined towards the indigo aperture in a 

 direction indicated by drawing a straight line from the plants 

 to the radiant. Not one plant inclined towards the red ray, 

 although half the collection were at first nearer to it than to 

 the more refrangible light. 



With similar arrangements, the yellow, orange, and green 

 rays were contrasted with the indigo, and always with the 

 foregoing result. The time necessary to develope a satisfac- 

 tory lateral inclination from the green rays, is greater than in 

 the experiments made between the less refrangible rays and 

 indigo. 



(24.) The same results were obtained when the radiants 

 were reflected images. The extent to which the influence of 

 the active light is felt was frequently surprising ; in some of 

 the observations pea plants were four feet from the indigo, 



