184 I). P. Pen/tallow — Tendril Movements in 



of the tissues themselves, through which variable tension is 

 most readily produced. We are thus led to the conclusion that 

 the collenchyma is the most important tissue of the entire 

 structure for the production of bending under the influence of 

 mechanical stimuli. 



A tendril subjected to local irritation for about thirty sec- 

 onds develops an abrupt curvature at that point within one or 

 two minutes, and not only continues to bend so long as the irri- 

 tating body is present, but even for a few seconds after its re- 

 moval. Puncture with a pin, or the action of a loop of 

 thread, produces the same effect. Irritation over considerable 

 length causes a longer curve for the same distance. There is 

 in all such results no evidence that the impulse has been con- 

 veyed to portions lying on either side of the irritated parts, 

 and very soon after the cause is removed the tendril straightens 

 out and resumes its circumnutations as before. A blow, how- 

 ever, produces a different effect. When given on any part of 

 the arm. the latter receives an impulse which extends through 

 its entire length, and instead of developing one long curve or a 

 single abrupt turn, it is thrown into a series of long waves. 

 Also, irritation at the tip produces the effect of a long curve 

 passing through the whole central region. These facts distinctly 

 show that the terminal portion is much more sensitive than 

 any other part of the tendril, and that irritation given there, or 

 imparted to other portions by percussion, is directly transmitted 

 through the entire length. That this transmission is accom- 

 plished through the protoplasm, which thus serves as the nerve 

 material, can no longer be doubted in view of the continuity 

 which we have shown to exist, coupled with the well known 

 sensitive nature of this substance. 



Circumnutation. — Our attention is first of all to be directed 

 to the fact pointed out by Darwin* and confirmed by our own 

 observations, that the " tendrils revolve by the curvature of 

 their entire length, excepting the sensitive tip and the base, 

 which parts do not move, or move but little." This clearly 

 shows that whatever force is in operation, acts uniformly 

 through the entire length of the whole motile organ, and that 

 the movement does not have a local origin at or near the base. 

 We must therefore conceive, as both Darwinfand Sachs^: ex- 

 plain, that there is a longitudinal band of tissue, or rather that 

 a line of cells extends from base to tip of the tendril, and that 

 this band, or these cells are in a more active state of growth 

 than those in other parts of the tendril, thus bending the latter 

 toward the opposite side. So far, our observations are in 

 strict harmony with these views; but they do not accord with 

 the opinions of these eminent authorities when they state that 



* ClimbiDg Plants, p. 170. f Ibid. % Text Book, p. 866. 



