300 PRINCIPLES OF GARDENING. [CH. YIII. 



during any check, is very much greater than coukl 

 have been expected, before Mr. Hales demonstrated 

 it by experiment. This distinguished vegetable 

 physiologist found, that in the vine this furce Avas 

 able to raise 19 lbs. weight. To the stem of a vine 

 cut off about two feet and a half from the ground, he 

 fixed a mercurial gauge, and luted it to the sides of 

 the stem with mastic. The gauge was in the form of 

 a syphon, so contrived, that the mercmy might be 

 made to rise in proportion to the pressure of the as- 

 cending sap. In this instance it raised the mercury 

 to a height of thirty-eight inches^. The branch of 

 an apple-tree was separated from the parent trunk, 

 and placed in water. When the leaves were upon it, 

 the force with which it propelled its sap, raised the 

 mercur}' four inches, in a tube attached as to the 

 vine; but a similar branch, deprived of its leaves, 

 scarcely raised the mercury a quarter of an inch. 

 The pear, quince, cherry, walnut, peach, gooseberry, 

 and sycamore, had a power equal to elevating the 

 mercur)% varying from three to six inches. The elm, 

 the oak, chesnut, hazel, sallow, and ash, elevated it 

 variously from one to two inches. The laurustinus, 

 laurel, and other evergreens, scarcelv raised the mer- 

 cury at all ^. 



The experiments made with a separated branch do 



* Hale's Vcget. Statics, vol. i. p. 107. 

 b Ibid. p. 114, &c. 



