40 Macfarlane. — Contributions to the History of 



Numerous such experiments were repeated with similar re- 

 sults, and others in which a series of summation stimuli were 

 communicated behaved in the ordinary way. The only par- 

 allel case to this that we know is that termed "contraction 

 remainder" in animal muscle, where namely as contracted 

 muscle is relaxing a weight applied to it will cause rapid and 

 permanent expansion. 



We may now attempt to unify the results already given. 

 We conclude that a leaf of Dioncea, previous to secretion, is 

 in a state of tetanic contraction. This tetanic state results 

 from a series of stimuli that may either be partially or entirely 

 mechanical, thermal, luminous, chemical, or electric. Tetanic 

 contraction of a leaf growing in the wild state, is due to two 

 mechanical stimuli by an animal, which thereby cause leaf 

 closure, succeeded by repeated mechanical stimuli as the 

 captured animal struggles to escape, and continued by numer- 

 ous chemical stimuli as the digested excretions of the animal 

 act on the gland protoplasm, and through it on the general 

 cell protoplasm of the leaf. 



Rarely it may happen in the wild state, but can readily be 

 demonstrated in the laboratory, that two rapidly applied 

 stimuli are propagated as one shock, and a third is then 

 needed to cause closure, the subsequent results being the 

 same. Any form of energy, alone or conjoined with others, 

 causes closure and tetanic contraction. 



Secretion succeeds tetanic contraction, though it is not 

 dependent on it, but the amount of secretion seems largely to 

 depend on the amount of stimulus. Thus, in the case of 

 leaves that secreted feebly when small cubes of roast meat 

 were placed on them, the absorption by, and stimulation of, 

 the protoplasm in the gland cells, through presence of nitro- 

 genous material, might be sufficient to cause activity in the 

 protoplasm that would set up a limited waste excretion. In 

 tetanic closure the stimulus being correspondingly greater, 

 the tissue waste exuding as a secretion is correspondingly 

 greater in amount. 



These phenomena are only explicable in terms of the pro- 

 toplasmic activity. From a careful study of like phenomena 



