OF INSECTIVOROUS PLANTS 431 



organisms which came from without the pitcher, and were not due to a 

 secretion of the plant. 



Couvreur (26) supported the conclusions of Dubois, and maintained 

 that the digestive phenomena observed by Vines were due to the action 

 of the reagents on each other, and not to the presence of a protease 

 in the pitcher liquor of Nepenthes. 



Tischutkin (27), in a paper on Pinguicula, commented on the work 

 of Von Gorup and Will. He considered that the protease, which these 

 investigators found in the pitcher liquor of Nepenthes, was entirely of 

 bacterial origin. 



Among the insectivorous plants studied by Tischutkin (10) was 

 Nepenthes Mastersi. The pitchers were stimulated by means of small, 

 sterile cubes of albumen. Even 24 hours later, the Uquor of the pitchers 

 contained myriads of bacteria, as was regularly shown by the direct 

 microscopic examination. The bacteria were isolated by cultures on 

 weakly acid nutrient gelatin and were tested for their peptonizing power; 

 several species were always found which dissolved small, sterile albumen 

 cubes fairly rapidly in an acidified menstruum. 



The following experiments were also carried out. Incisions were 

 made in the side wall of pitchers, which had not yet opened and therefore 

 contained no bacteria; the liquor was removed with a pipette and con- 

 veyed to test glasses which contained water and small cubes of albumen 

 (1 cube in each glass); in some glasses the water was neutral, in other 

 glasses it had been acidlied. The experiments were carried out with 

 antiseptic precautions. The results showed that the pitcher hquor did 

 not contain a peptonizing enz\Tne, for the substrate remained unchanged 

 after incubation for 48 hours at 37.5° C. In order to overcome the 

 possible objection that the pitchers had been too young, the experiments 

 were repeated in a modified form. Openings were made in the wall of 

 pitchers, which had not yet opened; small, sterile cubes of albumen were 

 introduced into the cavities of the pitchers; the openings were closed; 

 and the plants were permitted to remain undisturbed. When the pitchers 

 opened, ^ days later, the albumen cubes were found unaltered; their 

 angles had not been rounded off; the Hquor had a strongly acid reaction 

 and contained no peptone; and bacteria were present "in very shght 

 number." When the hquor of these pitchers was placed in test glasses 

 and treated anew with small cubes of albumen, it dissolved the cubes 

 only after 4 to 5 days had passed, i.e., at a time when the bacteria had 

 already multiplied to a considerable degree. 



