32 DARWINISM STATED BY DARWIN HIMSELF. 



weak hydrochloric acid, though almost any acid will 

 serve. Yet neither pepsin nor an acid by itself has 

 any such power. We have seen that when the glands 

 of the disk are excited by the contact of any object, es- 

 pecially of one containing nitrogenous matter, the outer 

 tentacles and often the blade become inflected ; the leaf 

 being thus converted into a temporary cup or stomach. 

 At the same time the discal glands secrete more copiously, 

 and the secretion becomes acid. Moreover, they trans- 

 mit some influence to the glands of the exterior tentacles, 

 causing them to pour forth a more copious secretion, 

 which also becomes acid or more acid than it was before. 

 As this result is an important one, I will give the 

 evidence. The secretion of many glands on thirty leaves, 

 which had not been in any way excited, was tested with 

 litmus-paper ; and the secretion of twenty-two of these 

 leaves did not in the least affect the color, whereas that of 

 eight caused an exceedingly feeble and sometimes doubt- 

 ful tinge of red. Two other old leaves, however, which 

 appeared to have been inflected several times, acted much 

 more decidedly on the paper. Particles of clean glass 

 were then placed on five of the leaves, cubes of albumen 

 on six, and bits of raw meat on three, on none of which 

 was the secretion at this time in the least acid. After 

 an interval of twenty-four hours, when almost all the 

 tentacles on these fourteen leaves had become more or 

 less inflected, I again tested the secretion, selecting glands 

 which had not as yet reached the center or touched any 

 object, and it was now plainly acid. The degree of 

 acidity of the secretion varied somewhat on the glands 

 of the same leaf. On some leaves a few tentacles did 

 not, from some unknown cause, become inflected, as 

 often happens ; and in five instances their secretion was 

 found not to be in the least acid ; while the secretion of 



