Dr Gardner on the Action of Light on Vegetables, 83 



experiment. The amount of bending frequently exceeds 

 ninety degrees ; and a movement of the fore extremity of the 

 stem through one inch, to one inch and a half from the perpen- 

 dicular, is not unusual in turnip seedlings. 



(19.) If the young plants be exposed to a spectrum, pro- 

 duced, as in art. 13, in a box without compartments, after a 

 time they will be found inclined diagonally towards a common 

 axis ; those in the red, orange, yellow, and green, bending to- 

 wards the indigo ; and the plants of the violet and lavender 

 spaces moving to meet them. When a larger spectrum of 

 fourteen inches was used, and the seedlings exposed for five 

 hours, they were so inclined as to suggest the appearance of a 

 field of growing wheat, blown by two winds to a common 

 point. If the experiment were sufficiently prolonged, some of 

 the plants from either side of the spectrum interlocked in the 

 direction of the axis. 



(20.) This axis is in the direction taken by Fraunhofer's 

 indigo ray^ in passing from the prisrn to the plants. The 

 seedlings growing in indigo light inclined directly along it j 

 but those of the red and orange did not move towards the 

 radiant in the prism, but along a diagonal, inclined in part to- 

 wards the plants illuminated by the active rays, which were 

 much nearer than the prism. The amount of this lateral in- 

 clination diminished as the plants were nearer the axis, so 

 that those illuminated by blue, violet, and lavender, were little 

 deflected from a line drawn from their place of growth to the 

 radiant. Seedlings in the red, orange, and yellow rays, frequent- 

 ly bent to such an extent as to cause their summits to pass 

 through the adjoining coloured space. 



(21.) The secondary (lateral) inclination did not occur when 

 the radiant was a reflected image of the spectrum, which was 

 not allowed to fall on any of the plants. If the mirror reflect- 

 ed neither of the more refrangible rays, the plants appeared to 

 be inclined to the light immediately before them. 



(22.) These experiments satisfied me that the active force 

 was in the indigo ray, and the intensity of the light necessary 

 to produce deflection was extremely feeble, so that an amount 

 inappreciable to the eye, which is an admirable measure of the 

 intensity, but incapable of estimating the effect of quantities, 



