SUPPLEMENT 151 



propagated to the other secondary petioles, the leaflets of which fold together, 

 the movement being from the base to the apex. Exceptionally the shock 

 stimulus may be transmitted as far as the primary articulation in which a 

 depression is induced. 



I. 42, after itself read from the primary root or from a lateral root. 



518, 1. 4, after concerned read; when these organs are stimulated by wound- 

 ing the rate of transmission of the stimulus is, according to FITTING (1903), 

 10 mm. per second. Haptotropic stimuli are transmitted over the same dis- 

 tance, in the most favourable instance, in 1-3 minutes. 



II. 6-17, for seeing that . . . vascular elements. PFEFFER read Careful 

 investigations into this highly remarkable phenomenon have been carried out 

 only with reference to stimulation by wounds. The stimulus in this case 

 appears to be transmitted solely by the vascular bundle. An incision made 

 into the stem has no effect unless the central cylinder in which the vascular 

 bundle lies is affected, but after every wound capable of inducing stimulation 

 one sees a drop of fluid escaping from the central cylinder. On the basis of 

 such observations PFEFFER 



11. 24-7, for If an incision . . . place in them, read The effect of anaesthe- 

 tizing and killing short stretches of the conductive strands supports the view 

 that the stimulus is transmitted by means of mechanical media of this kind. 

 As PFEFFER (1873 b) and HABERLANDT (1890) were able to show, stretches 

 thus altered could still transmit the stimulus, a fact which completely excluded 

 the co-operation of living cells in the process. According to FITTING'S more 

 recent results, however, there is a difference between stimulus conduction in 

 uninjured stems and in those subjected to the temperature of boiling water : 

 in the latter case the stimulus is transmitted backwards only, in the former 

 both ways, and hence it follows that the conduction is effected in dead cells 

 in another manner than in living ones. PFEFFER believed in a variation in 

 pressure in the vessels, and regarded the fluid exuded from them as water. 

 He based his view on an experiment of DUTROCHET'S (1837), ^ n which the 

 stimulus was still transmitted through regions of the stem from which the 

 cortex had been removed. 



1. 41, for hyphae read cells 



1. 43 P. 519, 1. 41, for The one criticism ... in dispute.] read Several 

 criticisms may be advanced against HABERLANDT'S conception, of whiph the 

 following are the most important (FITTING, 1903, 1906). The tubular cells 

 with their closed walls, which are pierced only by very fine protoplasmic 

 threads, are not well adapted for the rapid transmission of streams of water, 

 nor has it been found possible to accelerate such streams artificially by sub- 

 jecting them to greater pressure. More important still is the fact that many 

 plants, more especially Neptunia, a genus very closely allied to Mimosa, 

 possess no such tubular cells, and the secondary roots of Mimosa itself are 

 also destitute of them, although they are capable of transmitting a stimulus 

 induced by wounding. Finally, it appears, according to FITTING'S observa- 

 tions, that the wound stimulus in tendrils corresponds exactly with that in 

 Mimosa here also stimulation takes place only if the central cylinder be cut 

 into, and here also drops of fluid escape. The fluid in the case of the tendrils, 

 however, escapes from the sieve-tubes tubular cells are entirely wanting. It 

 would thus appear as though the sieve-tubes were the conductive agents in 

 Mimosa also, and their distribution in the plant is not out of accord with that 

 view, and, further, their open pores would appear to adapt them much better 

 for such a function. 



If, then, the transmission of the stimulus in Mimosa and related cases is 

 effected by fluid currents in sieve-tubes, we should have to deal with a mode 



