Dr. Gardner on the Action of Light upon Vegetables. 9 



the deflecting force. For this purpose, the spectrum was allowed 

 to fall upon a screen, perforated by two similar apertures, in such 

 positions as to allow the red ray to pass through one, and the in- 

 digo through the other. Behind the screen, a box was placed 

 containing four jars of turnip seedlings, arranged along a line oc- 

 cupying 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 extremity. All the plants 

 commenced bending in a short time, and in two hours the near- 

 est 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 jar. 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 aper- 

 ture, 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 satisfactory lateral in- 

 clination 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 ac- 

 tive light is felt was frequently surprising ; in some of the obser- 

 vations pea plants were situated four feet from the indigo, and 

 within half an inch of the yellow, red or orange radiant, notwith- 

 standing which, they inclined towards the indigo. In these re- 

 searches, the mirror was so situated as to reflect no prismatic 

 light upon the plants. 



(25.) That no doubt may rest, on the place of the soliciting 

 force, another arrangement was used. The instrument figured 

 by M. Pouillet, (Elemens de Phys., &c. t. 1, fig. 218,) for exam- 

 ining the effect of combinations of rays of light in producing color, 

 was taken. Red rays were received on one mirror, and indigo 

 on another, and the two so far inclined as to cause the rays to in- 

 termix at a place about three inches in advance of the instrument, 

 and out of the incident beam. A jar of turnip seedlings was then 



Vol. xlvi, No. 1.— Oct.-Dec. 1843. 2 



