112 



Lord Rayleigh. 



stitute a factor, which cannot fail to have an important bearing 

 in all general questions, such as the growth of the cell wall, the 

 conduction of food, the ascent of water, the process of fertilisation, 

 the penetration of fungi into their host, the process of secretion, and 

 the transmission of the impulses which determine growth and move- 

 ment of plant organs. 



Concerning certain of these problems, I should like to make a few 

 concluding remarks. 



As to the passage of water from the root hair to the vessel, the 

 presence of connecting threads in the cells of root tissue makes it 

 possible to imagine that the ordinary laws of osmosis may be pro- 

 foundly modified, and that the filaments which establish protoplasmic 

 continuity may conduct stimuli, leading, for instance, to a difference 

 in reaction of the proximal and distal halves of any given cell. 

 Similarly, it is conceivable that a definite polarity is established, 

 which helps to determine the direction of the flow. As to the larger 

 question of rapid water movement, although this is neither the time 

 nor the place to enter into theory, yet I cannot refrain from remark- 

 ing that it is not impossible that the threads, doubtless present in 

 large quantities in dead vessels, may, if they suffer mucilaginous 

 change, have some bearing on the question, e.g., by assisting to 

 sustain the water at any given level or attracting water in the imme- 

 diate environment. In any case, I am strongly of opinion that the 

 part played by mucilage and the force of hydration have not as yet 

 received sufficient attention. 



As to movements generally, I am still unable to accept Pfeffer's 

 view of the subsidiary part played by the protoplasm in connexion 

 with turgidity* and I am still of opinion that the ectoplasm is the 

 master factor which determines the condition of the cell. The present 

 research demonstrates among other things that there are fixed points 

 in the ectoplasm, and this may have some bearing on the possibility 

 of establishing the periodic or sudden contractions and dilatations 

 which I believe are associated with ttirgescence, and of which such a 

 phenomenon as the effusion of water from the cells of a stimulated 

 Mimosa pulvinus is but an abnormal instance. 



" On the Viscosity of Hydrogen as affected by Moisture." By 

 Lord Rayleigh, F.R.S. Received September 8, 1897. 



In Sir W. Crookes's important work upon the viscosity of gasesf 

 the case of hydrogen was found to present peculiar difficulty. 

 " With each improvement in purification and drying I have obtained 



* Gardiner, ' Roy. Soc. Proc.,' vol. 43, 1887. 

 f ' Phil. Trans.,' 1881, p. 387. * 



