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



will be found inclined diagonally towards a common axis — those 

 in the red, orange, yellow, and green, bending towards the in- 

 digo, 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 in- 

 clined 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 Fraunhofef s indigo 

 ray in passing from the prism to the plants. The seedlings 

 growing in indigo light inclined directly along it ; but those of 

 the red and orange did not move towards the radiant in the 

 prism, but along a diagonal, inclined in. part towards the plants 

 illuminated by the active rays, which were much nearer than 

 the prism. The amount of this lateral inclination 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, or- 

 ange, and yellow rays, frequently bent to such an extent, as to 

 cause their summits to pass through the adjoining colored 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 reflected 

 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 pro- 

 duce deflection was extremely feeble, so that an amount inap- 

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

 intensity, but incapable of estimating the effect of quantities, 

 would after a lengthened exposure, cause considerable deflection. 

 Indeed the phenomenon is so little dependent on the brilliancy of 

 light, that very little seems to be gained by concentrating the 

 rays beyond a certain point. There is sufficient activity in each 

 prismatic color to produce bending, if enough time be allowed. 

 The movement is therefore a result depending upon the absorp- 

 tion of light. 



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

 ent to advance some further evidence concerning the position of 



