Plate 19. — Illustrating a radiograph of 

 plant tissue. — A contact radiograph of a 

 young leaf removed from the plant 36 hours 

 after introducing the P^d into the nutrient 

 solution. The time of exposure was one hour. 

 The light areas, a, b, c, d, were caused by folds 

 in the leaves and e by the bunching of several 

 small leaflets. (From Arnon, Stout, and 

 SiPOS, 1940). 



