STEPHEN HALES 131 



this difference, being satisfied of "great quantities 

 of liquor having passed laterally by the gap." 



He is interested in the fact of lateral trans- 

 mission in connexion with the experiment of the 

 suspended tree (Fig. 24, p. 126), which is dependent 

 on the neighbours to which it is grafted for its 

 water supply. This seems to be one of the results 

 that convinced him that there is a distribution of 

 food material which cannot be described as circula- 

 tion of sap in the sense that was then in vogue. 



Hales (p. 143) was one of the first^ to make the 

 well-known experiment — the removal of a ring of 

 bark, with the result that the edge of bark nearest 

 the base of the branch swells and thickens in a 

 characteristic manner. He points out that if a 

 number of rings are made one above the other, the 

 swelling is seen at the lower edge of each isolated 

 piece of bark, and therefore (p. 143) the swelling 

 must be attributed "to some other cause than the 

 stoppage of the sap in its return downwards," 

 because the first gap in the bark should be sufficient 

 to check the whole of the flowing sap.^ He must, 

 in fact have seen that there is a redistribution of 

 plastic material in each section of bark. 



We now for the moment leave the subject of 

 transpiration and pass on to that of root-pressure 

 on which Hales is equally illuminating. 



^ He refers (p. 141) to what is in principle the same experiment 

 (see Fig. 27) as due to Mr. Brotherton, and pubUshed in the Abridge- 

 ment of the Phil. Trans. 11. p. 708. 



' He notices that the sweUing of the bark is connected with 

 the presence of buds. The only ring of bark which had no bud 

 showed no swelUng. 



