Francis E. Lloyd — 144 — Carnivorous Plants 



cases small and uniformly sized objects for stimulation, viz., the eggs 

 of the wood-louse. 



The responses of the strictly marginal ("outer marginal") tentacles 

 are somewhat slower than those standing just within the margin ("in- 

 ner marginal")- Their reaction to a direct stimulus (that is, one ap- 

 plied to the glands of these tentacles) is, however, always strictly 

 nastic; their function is to bring the prey into contact with the discal 

 glands. The sensitivity and quickness of reaction are surprising. The 

 reaction may begin in lo seconds, and was seen to make a complete 

 excursion of i8o degrees in 20 seconds, the movement being visible to 

 the naked eye. This was a maximum, however. It must be clear that 

 the direction of movement is in a single plane normal to the leaf mar- 

 gin. Prompt and rapid as their response to direct stimulus is, they re- 

 spond to indirect stimulus, derived from stimulated discal tentacles, 

 only slowly and weakly. At best, a reaction may be detected in 10 

 minutes, but the total excursion is short. Only when the leaf is heavily 

 fed, especially with living prey, do the marginal tentacles indirectly stim- 

 ulated actually reach the prey. If the stimulus is derived from a small 

 insect, the excursions of the marginal tentacles are incomplete, are soon 

 reversed and can be of no use to the plant, though, since complete 

 bendings can occur only three times at best, the meagreness of re- 

 sponse may be regarded as an economy of effort. Full expenditure of 

 effort is made only when the prey falls on the marginal tentacles, when 

 by bending fully they bring it into contact with the inner tentacles 

 thus exposing it to much greater digestive surface. The movements 

 are at first nastic. Since in D. rokmdifolia the orbicular form of the 

 leaf results in nastic and tropistic reactions acting in the same direc- 

 tion, the observer is and has been naturally deceived. Only when the 

 reactions are observed in such leaves as those of D. intermedia and D. 

 binata is it seen clearly that, while the reaction of the marginal ten- 

 tacles to direct stimulation is at first nastic, in the course of the ex- 

 cursion the direction of movement may be modified by tropistic re- 

 actions, especially clear in D. binata, and in this is the account of 

 Hooker amplified. 



In the case of the central or discal tentacles, there is no response to 

 direct stimulus, that is, stimulating material placed on a single tentacle 

 produces no movement in that tentacle. But the stimulus is quickly 

 transmitted to nearby tentacles and these then bend toward the point 

 of stimulation, that is tropistically. The rate of reaction is here much 

 more dependent on temperature — from an hour to 20 or so, according 

 to circumstances. 



Between the central disc tentacles and the marginal lies a narrow 

 zone of outer surface tentacles, in size grading between them, being in 

 such species as D. binata as long as the marginal tentacles, or longer. 

 Their reactions are more complicated than those of the tentacles of the 

 other two zones, since they combine properties of both. They react 

 nastically to direct stimulus and as rapidly as the marginal tentacles, 

 and this character distinguishes them at once from the central disc 

 tentacles. Toward indirect stimulus their reactions are both nastic and 

 tropistic, and the resulting excursions are rapid and more extended than 

 those of the marginal tentacles to indirect stimulus, and result in bring- 



