BOTANICAL ADDRESS TO THE BRITISH ASSOCIATION. 11 



hoped is a general agreement amongst the staffs of the 



principal institutions in different countries where systematic 



botany is worked at; the free-lances must be left to do as 



they like. 



Vegetable Physiology. 



In an address which I delivered at the Bath meeting in 

 1888, I ventured to point out the importaut part which the 

 action of enzymes would be found to play in plant meta- 

 bolism. My expectations have been more than realized by 

 the admirable work of Professor Green on the one hand, 

 and of Mr. Horace Brown on the other. The wildest 

 imagination could not have foreseen the developments 

 which in the hands of animal physiologists would spring 

 from the study of the fermentative changes produced by yeast 

 and bacteria. These, it seems to me, bid fair to revolutionize 

 our whole conceptions of disease. The reciprocal action of 

 ferments, developed in so admirable a manner by Marshall 

 Ward in the case of the ginger-beer plant, is destined, I am 

 convinced, to an expansion scarcely less important. 



We owe to Mr. Blackman a masterly demonstration of the 

 fact, long believed, but never perhaps properly proved, that 

 the surface of plants is ordinarily impermeable to gases. 

 Mr. Dixon has brought forward some new views about water- 

 movement in plants, which I confess I found less instructive 

 than many of my brother botanists. They are expressed in 

 language of extreme technicality; but, as far as I under- 

 stand them, they amount to this. The water moving in the 

 plant is contained in capillary channels; as it evaporates at 

 the surface of the leaves, a tensile strain is set up, as long as 

 the columns are not broken, to restore the original level. I 

 can understand that in this way the ' transpiration current ' 

 may be maintained. But what I want to know is, how this 

 explains the phenomena in the sugar maple, a single tree of 

 which will yield, I believe, 20-30 gallons of fluid before a 

 single leaf is expanded. 



We owe to Messrs. Darwin and Acton the supply of a 

 ' Manual of Practical Vegetable Physiology,' the want of 



