Dr Gardner on the Action of Light on Vegetables. 85 



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

 notwithstanding which they inclined towards the indigo. In. 

 these researches, 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 {FAemens de Phys., t. i. fig. 218) for examining 

 the effect of combinations of rays of light in producing colour, 

 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 in- 

 strument, and out of the incident beam. A jar of turnip 

 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 was inclined directly to taht radiant. 

 Those which received red light were bent to the central pur- 

 ple, and none to the red radiant. But many seedlings at first 

 in the red, inclined themselves towards the purple, and after 

 being fully illuminated thereby, commenced a lateral move- 

 ment towards the indigo radiant ; so that, at the close of the 

 experiment, their stems exhibited two inclinations, the one in 

 a vertical, and the other in a horizontal plane. 



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

 green, were used in the preceding observations ; but the sen- 

 sibility of the former gi-eatly exceeds that of the latter. In- 

 deed, plants that have been exposed to light for several days, 

 become sluggish in their movements, and the phenomenon 

 probably ceases in parts which are ligneous. In the seedlings 

 submitted to examination the movements were found to take 

 place in consequence of an action impressed upon the stem 

 only ; for the removal of the leaflets did not alter the result. 

 A still more remarkable fact was discovered in all the cases 

 observed — that after complete bending, plants erect them- 

 selves again when placed in darkness, at least in situations so 

 dark as to appear entirely deprived of light. This effect is 

 best seen in seedlings which have never been exposed to the 

 direct rays of the sun ; for, after full and lengthened exposure 



