CHAP. XVI. SECRETION, ABSORPTION, DIGESTION. 381 



bearing on our subject, that when a plant is pulled 

 up, the leaves immediately curl downwards so as 

 almost to conceal the roots, a fact which has been 

 noticed by many persons. I suppose that this is due 

 to the same tendency which causes the outer and older 

 leaves to lie flat on the ground. It further appears 

 that the flower-stalks are to a certain extent irritable, 

 for Dr. Johnson states that they "bend backwards if 

 rudely handled." * 



Secretion, Absorption, and Digestion. I will first give 

 my observations and experiments, and then a summary 

 of the results. 



The Effects of Objects containing Soluble Nitrogenous Mutter. 



(1) Flies were placed on many leaves, and excited the glands 

 to secrete copiously ; the secretion always becoming acid, though 

 not so before. After a time these insects were rendered so 

 tender that their limbs and bodies could be separated by a 

 mere touch, owing no doubt to the digestion and disintegration 

 of their muscles. The glands in contact with a small fly con- 

 tinued to secrete for four days, and then became almost dry. 

 A narrow strip of this leaf was cut off, and the glands of the 

 longer and shorter hairs, which had lain in contact for the 

 four days with the fly, and those which had not touched it, 

 were compared under the microscope and presented a won- 

 derful contrast. Those which had been in contact were filled 

 with brownish granular matter, the others with homogeneous 

 fluid. There could therefore be no doubt that the former had 

 absorbed matter from the fly. 



(2) Small bits of roast meat, placed on a leaf, always caused 

 much acid secretion in the course of a few hours in one case 

 within 40 m. When thin fibres of meat were laid along the 

 margin of a leaf which stood almost upright, the secretion ran 

 down to the ground. Angular bits of meat, placed in little 

 pools of the secretion near the margin, were in the course of 



* ' English Botany,' by Sir J. E. Smith ; with coloured tiguros by 

 J. Sowerby ; edit, of 1832, tab. 24, 25, 20. 



