Francis E. Lloyd —76— Carnivorous Plants 



was used. This is interpreted as demonstrating that the addition of a 

 protein to the fluid stimulates the secretion of acid; but de Zeeuw was 

 unable to bring this about by mechanical stimulation, the contrary 

 having been reported by Hepburn {see above). The secretion of un- 

 opened pitchers had been found by de Kramer to be always neutral, 

 and this was re-examined by de Zeeuw who found the pH ranging 

 from 4.2 to 7 (ave. 6.6 ± 1.2) in October and from 4.2 to 4.8 (ave. 

 4.5 + 0.3) in November and December, a difference possibly attribut- 

 able to the time of year, with a lower temperature prevailing (in the 

 greenhouse?). The fluid of pitchers opened under sterile conditions, 

 therefore without chemical stimulation, always reacted acid (pH 4.2 to 

 5.8) but required additional acid to secure digestion. When acidified to 

 pH 3.0 to 3.5 with certain acids (phosphoric, HCl, formic, malic, 

 and succinic acid), and kept sterile with toluene, digestion proceeded, 

 but not with the others tried, which probably destroyed the enzyme. 

 What kind of acid is secreted by the pitcher, aside from the fact that it 

 is not a volatile one, was not determined. But the acid reaction of the 

 glands indicated that these are responsible. De Zeeuw therefore 

 reached the conclusion that the enzymes present are catheptic and 

 tryptic, but that the former only is present in sterile pitcher fluid, the 

 latter occurring only in opened pitchers to which bacteria had had 

 access. Acid is secreted by the gland when stimulated by chemical 

 but not by mechanical means. 



As the matter stands at the present, therefore, the positive evidence 

 that a catheptic proteinase is secreted by the pitchers of Nepenthes is 

 conclusive. That tryptic digestion in the absence of bacteria takes 

 place there seems little doubt, but this cannot yet be said to be com- 

 pletely proven. 



Antisepsis of pitcher fluid. — Reference has been made to the fact, 

 usually accepted as such, that the pitcher fluid of normal actively di- 

 gesting pitchers is free of bacterial action. Wallace has already been 

 quoted as testifying to this in the natural habitat in Borneo. Goebel 

 atributed this, in the experiments he conducted, to the presence of for- 

 mic acid secreted by the pitcher glands. Robinson (1908) observed 

 that meat extract might remain in the pitchers of N. destillatoria for 

 two weeks without the odor of foulness. Although they confirmed the 

 generally accepted belief that the fluid of unopened pitchers is sterile, 

 Hepburn et al. (1919, 1927) found that opened pitchers, whether 

 containing insects or not, invariably contained bacteria in large num- 

 bers, whose activity in digesting proteins they found was low, and that 

 they play only a secondary role in the digestion of insects, the leading 

 role being played by the protease proper to the pitcher itself. They 

 argued that the bacteria five in symbiosis with the plant, assisting some- 

 what in the digestion of insects, thereby drawing nutrition therefrom. 

 Since the plants they experimented with were under cultivation, the 

 argument that their results do not reflect the conditions found in 

 nature, as indicated by such experiences as Wallace, seems justified. 

 Testimony is, however, not uniform on this point. Jensen (1910) speaks 

 twice of the horrible stench arising from pitchers loaded with centi- 

 pedes, cockroaches, butterflies and a huge scorpion found in pitchers 

 near Tjibodas, Java. This may mean merely that the pitchers were 



