226 Prof. H. E. Armstrong and Dr. E. F. Armstrong. [June 29, 



•of its maximal value.* This agrees with the fact that down to a diameter 

 of 500 fi/u, the velocity still appears to be independent of size aud shape. 



It may be well, in conclusion, to emphasise the significance of the 

 experiments. They seem to prove either that the coefficient of sliding 

 friction between two phases is independent of the Laplacian pressure at 

 the interface, or that the range of the molecular attraction is much less 

 than Kiicker's estimate — 50 jifi. 



[P.S., added July 30. — During the present hot weather, when the water 

 in the laboratory stands at 28° C, the film was found to have diminished 

 in tenacity to a great extent. In order to give it the same degree of fixity 

 under electrical stresses which it possessed at temperatures between 15° 

 and 20°, it had to be thickened with oil until a blue film was produced, 

 which almost entirely stopped the movements of camphor.] 



The Origin of Osmotic Effects. IV. — Note on the Differential 

 Septa in Plants ivith reference to the Translocation of 

 Nutritive Materials. 



By Henry E. Armstrong, F.R.S., and E. Erankland Armstrong. 



(Eeceived and read June 29, 1911.) 



Our communication to the Society which was read on June 2 last yearf 

 was made under the primary title attached to the present communication, 

 because it appeared to us that many of the osmotic phenomena in plants 

 were to be correlated with effects produced initially by the class of substances 

 to which we have ventured to extend the term Hormone, introduced by 

 Starling but applied by him only to certain members of the group. The 

 observations recorded were made with leaves of Prunus lavrocerasus. In a 



* The integral for the pressure at the surface of a sphere in a vacuum is given by 

 Eayleigh ('Phil. Mag.,' 1890 [2], vol. 30, p. 456), as 2tt j ~'f-n{f) df-^ | */%(/) df. 



Putting tt(/) = ^e-p/, this reduces to [e-2tf( 4 I + 8 I + 6-L) -6-^ + 4^] . 



+ " The Origin of Osmotic Effects. III. — The Function of Hormones in Stimulating 

 Enzymie Change in Eelation to Narcosis and the Phenomena of Degenerative and 

 Regenerative Change in Living Structures," 'Roy. Soc. Proc.,' B, 1910, vol. 82. 



