562 Mr. Horace T. Brown on Diffusion. [March 22, 



minute stomates as the sole pathways of gaseous exchange in the 

 leaf entirely disappear when the leaf is studied in this new light, 

 and it becomes evident that the adjustment of the mechanism of the 

 leaf to the physical properties of its surrounding medium is far more 

 perfect than has been hitherto suspected. The leaves of plants have 

 in fact proved themselves better physicists than ourselves, since their 

 structure bears the impress of response to certain properties of gases 

 of which wo have hitherto been ignorant. 



This is by no means the first occasion on which the plant has 

 given us a lead in physics. The theory of dilute solutions, formu- 

 lated by Van't Hoff, and indicating that the laws of Boyle and of 

 Avogadro are as applicable to dilute solutions as they are to gases, 

 had its origin in the observations of De Vries and of Pfeffer on the 

 plasmolysis of living cells and the properties of natural semi- 

 permeable membranes. 



Nor can we doubt that there are many more such instances which 

 only await detection, and we may reasonably hope that the boundaries 

 of physics and of chemistry will be materially enlarged in unexpected 

 directions if we pay due regard to the whispered hints and slender 

 clues which are on all sides given by the living world of Nature. 



[H. T. B.] 



