The Action of Plants on a Photographic Plate in the Dark. 385 



1 hour. 3 hours. 24 hours. 



Ethylic tartrate 0-9 12 1-8 



malate 270 57 16 



succinate 13-50 14-5 20-4 



We have to thank Mr. K. E. Armstrong, B.A, for valuable assistance 

 rendered in the latter part of the inquiry. 



The Action of Plants on a Photographic Plate in the Dark. 

 By W. J. Russell, Ph.D., F.E.S. 



(Received June 19, — Read June 28, 1906.) 

 [Plates 19-21.] 



It has been shown in former papers that wood has the property of acting 

 in the dark on a photographic plate, when placed in contact or in proximity 

 to it. Not only does wood act in this way, but leaves, seeds, roots, bulbs, 

 and, in fact, with only few exceptions, all vegetable substances act in a 

 similar way. The more important bodies which are without this property 

 are starch, cellulose, gum, sugar, pith, and pollen. To obtain this action on 

 a plate it is necessary that the body used be tolerably dry, or else the 

 moisture contained in it will act on the gelatine of the photographic plate 

 and destroy the picture. The time necessary for the exposure to the plate 

 varies from a few minutes to 18 hours or more. To quicken the action, heat 

 may be applied, but the temperature must not be above 55° C, nor the time 

 of exposure, under ordinary circumstances, longer than 18 hours, or the 

 photographic film will be injured. Any ordinary rapid photographic plate 

 may be used, and its development is exactly the same as that of an ordinary 

 picture. The best and most general method of drying vegetable substances 

 before exposing them to the photographic plate is to place them between 

 pure white blotting paper and subject them to considerable pressure, say 

 from 1 to 5 or 6 tons per square inch. This process has also the advantage 

 of giving a second picture, for it is found that the liquid which has been 

 expressed and absorbed by the blotting paper is capable of acting on a 

 photographic plate, and that it gives a good representation of the plant 

 from which it came (Plate 19, fig. 1, an oak leaf). 



Since different woods are capable of acting on a photographic plate it was 

 to be expected that leaves, stems, flowers would do the same. This has 



2 G 2 



