THE NUTRITION OF HETEROTROPHIC PLANTS 



185 



the chemical stimulus resulting from the presence of a digestible substance. 

 As yet, however, we know very little either about the enzyme or the acid. 

 According to one account, formic acid is declared to be present, but more recently 

 this has been denied. VINES'S (1897-1902) discovery that Nepenthes excreted 

 a tryptic ferment has been lately questioned by CLAUTRIAU (1900), who thought 

 he had proved the presence of a pepsin. It is true that minute particles of meat, 



Fig. 34. Leaf of Dionaea musciputa. When the hairs on the 

 upper side of the leaf are touched the two half blades instantly come 

 together. (From the Bonn Textbook.) 



Fig. 33. Pitcher of Nepen- 

 thes^ partly cut open to show 

 contents. The basal region is 

 occupied by a fluid excreted 

 from special glandular hairs in 

 which the animals which fall 

 into the pitcher are digested. 

 From the Bonn Textbook.) 



Fig- 35- Utrtcularia vulgaris. A^ portion of the leaf with blad- 

 ders ; B, portion of a leaf with bladder ; C, bladder in longitudinal 

 section (x 28) ; v, trapdoor; a, wall ; /, central cavity, (frrom the 

 Bonn Textbook.} 



fibrin, &c., are dissolved rapidly by Nepenthes and by Drosera, and that, too, 

 certainly without the help of Bacteria. Many of the secretions of carnivorous 

 plants have, in addition, antiseptic characters, so that micro-organisms are 

 quite unable to exist in them. 



The products resulting from the dissolution of proteid are absorbed either 

 by the secretory hairs which produce the enzyme or by other special trichomic 

 structures. Digestion and absorption take place often very rapidly. Thus 

 DARWIN (1876) observed that small cubes of white of egg were dissolved in the 

 course of one or two days, and that the gelatinous fluid resulting was com- 

 pletely absorbed in about three days. 



