CHAP. I. FOOD AND DIGESTION. 41 



The cells with chlorophyll next lose more or 

 less completely their green colour, and their 

 contents finally become brown. The parts 

 thus affected often appeared almost black by 

 reflected light ; but when viewed as a trans- 

 parent object under the microscope, minute 

 specks of light were transmitted, arid this 

 was not the case with the unaffected parts 

 of the same leaves. These effects, how- 

 ever, merely show that the secreted fluid is 

 highly injurious or poisonous to leaves ; for 

 nearly the same effects were produced in from 

 one to two days on various kinds of young 

 leaves, not only by artificial pancreatic fluid, 

 prepared with or without thymol, but quickly 

 by a solution of thymol by itself. On one 

 occasion leaves of Corylus were much dis- 

 coloured by being kept for eighteen hours in 

 pancreatic fluid, without any thymol. With 

 young and tender leaves immersion in human 

 saliva during rather warm weather, acted in 

 the same manner as the pancreatic fluid, but 

 not so quickly. The leaves in all these 

 cases often became infiltrated with the 

 fluid. 



Large leaves from an ivy plant growing 



