152 PLANT PHYSIOLOGY 



of transmission widely different from that already met with, e.g. in heliotropic 

 stimulus conduction. In that case what was transmitted from cell to cell 

 was the protoplasmic condition induced by the stimulus at some particular 

 region ; here it is the stimulus itself that is transmitted ; the movement of the 

 fluid can scarcely operate in any other way than by affecting the sensitive 

 pulvinus and causing a vibration in it, like a shock from without. There are 

 not wanting arguments against this conception, however. First of all it must 

 be noted that tendrils are quite insensitive to blows striking them from without, 

 and it is not quite conceivable why blows arising internally, associated with 

 the water displacement, should induce a stimulation (FITTING, 1906). Further, 

 HABERLANDT has found that the stimulus is propagated over a stretch of 

 tissue which really includes the whole rind with sieve-tubes and tubular cells. 

 HABERLANDT has attempted to harmonize this at first sight somewhat incon- 

 venient observation with his own theory, by aid of a subsidiary hypothesis, 

 but it is first of all necessary to determine whether the observation itself is 

 correct FITTING was unable to confirm it. FITTING, however, advances 

 another observation which tells against the view that a displacement of fluid 

 in the sieve-tubes is the cause of the conduction of the stimulus. There are 

 many plants (Neptunia, Biophytum, tendrils of many Cucurbitaceae) where 

 no extrusion of drops can be observed in spite of vigorous and rapid stimula- 

 tion, but such an extrusion must be demonstrable if there be a streaming in 

 the sieve-tubes. Hence we are unable to offer any final and logical explana- 

 tion of this process, notwithstanding the frequency with which it has been 

 studied. 



We cannot say whether the conduction of a stimulus after rubbing corre- 

 sponds with that after wounding, but FITTING (1906, p. 246) has shown that 

 to assume that here also there is a purely mechanical transmission of the 

 stimulus lands us in even greater difficulties than those we met with in discussing 

 stimulus due to wounding. 



519, 1. 55, after stimulus, read According to^LiSBAUER (1905) the contraction 

 begins in less than a second after contact in the very sensitive filaments of 

 C. americana. The contraction is completed in 7-13 seconds, and in 50-60 

 seconds afterwards the filaments have regained their original length, and have 

 again become capable of stimulation. 



520, 1. 48, for 1897 read 1887 



521, Lecture XLI is XL of the 2nd German Edition. 



1. 51, after yet done read (comp. especially PFEFFER, 1893 ; NOLL, 

 1896 ; FITTING, 1905-7). 



522, 1. 7, for I, 9 and II, 80 read I, 10 and II, 74 



523, 1. 45 P. 524, 1. 21, for Just as we ... etiolation, read The plant is, how- 

 ever, more complicated in many ways than the simple machine, the electric 

 arrangement, which has served as our illustration of a releasing stimulus. 

 Should we desire to pursue the comparison with the plant further still, we 

 must not only suppose that our model has different keys corresponding to 

 different external influences, but we must also assume that the released current 

 can do something more than set a bell in motion ; we must grant the possi- 

 bility of its acting on a glow lamp or a voltameter. If we assume that the 

 current may at one time pass through one, at another time through another 

 of these pieces of apparatus, our mechanical model will perform quite different 

 work according to the conditions. The introduction of one or other of the 

 three pieces of apparatus in the circuit might be effected by external agency 

 or by internal conditions of the mechanism itself. As regards external agencies, 



