8 Dr. Gardner on the Action of Yellow 



the further extremity. All the plants commenced bending in 

 a short time, and in two hours the nearest groups were in- 

 clined forwards 90°, and laterally 50° towards the indigo aper- 

 ture, 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 §\ hours, 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, ttot a plant inclined towards the red ray, 

 although half the collection were nearer to it than to the more 

 refrangible light. 



With similar arrangements, the yellow, orange and green 

 rays were examined in contrast with the indigo, with the fore- 

 going result in every case. The time necessary to develope 

 a satisfactory 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 produced 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 situated four feet from the indigo 

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

 notwithstanding which they inclined towards the most refran- 

 gible rays. In these researches the mirror was situated so 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, tome i. fig. 218) for 

 examining the effect of combinations of rays of light in pro- 

 ducing colours 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 intermix at a place about three inches in 

 advance of the instrument. A jar of turnep-seedlings was then 

 placed so as to receive the compound light in its centre, the 

 plants being illuminated in part by the red, indigo and purple 

 rays. In two hours the movements were considerable and 

 somewhat complex. Every plant lighted by the indigo rays 

 were inclined directly to that radiant. Those which received 

 red light were bent to the central purple, and none to the red 

 radiant. But many seedlings at first in the red inclined them- 

 selves towards the purple, and afterwards, having become 

 fully illuminated thereby, commenced a lateral movement to- 

 wards the indigo radiant, so that, at the close of the experi- 

 ment, their stems exhibited two inclinations, one in a vertical 

 and the other in a horizontal plane. 



26. Plants raised in darkness, as well as those which were 



