I30 STEPHEN HALES 



that one branch was inverted out of respect for the 

 hypothesis of sap-circulation. He perhaps thought 

 that water could travel apically by the wood, but 

 only by the bark in the opposite direction. 



Next in order (p. 95) comes his well-known 

 experiment on the pressure exerted by peas in- 

 creasing in size as they imbibe water. There are, 

 however, pitfalls in this result of which Hales was 

 unaware, and perhaps the chief interest to us now 

 is that he considered the imbibition of the peas^ 

 to be the same order of phenomenon as the absorp- 

 tion of water by a cut branch — notwithstanding 

 the fact that he knew the absorption to depend 

 largelyon the leaves.^ It may be noticed that Sachs, 

 in his imbibitional view of water-transport, may be 

 counted a follower of Hales. 



In order to ascertain "whether there was any 

 lateral communication of the sap and sap vessels, 

 as there is of blood in animals," Hales (p. 121) made 

 the experiment which has been repeated in modern 

 laboratories,' i.e. cutting a "gap to the pith," and 

 another opposite to it and a few inches above. 

 This he did on an oak branch six feet long whose 

 basal end was placed in water. The branch con- 

 tinued to "perspire" for two days, but gave off 

 only about half the amount of water transpired by a 

 normal branch.* He does not trouble himself about 



* The method by which Hales proposed to record the depth of 

 the sea is a variant of this apparatus. 



* Vegetable Staiichs, p. 92. 



* According to Sachs (Geschichte, p. 509) Ray employed this 

 method. 



' Other facts showed that the " gapped " branches did not 

 behave quite normally. 



