THE VEGETABLE KINGDOM. 381 



violently into the vessels of large animals is not driven with 

 so much power as impels the sap in its ascending move- 

 ment. Indeed, experiments made on the ox and horse 

 have shown that the impulse given to the arterial blood 

 would only raise a column of blood about six and one half 

 feet; the advantage is therefore not at all on the side 

 where it was supposed to be, since, according to what has 

 been already stated, the vegetable circulation raises a 

 weight fourteen times greater than does that of the lar- 

 gest mammals. 



Thus there are vessels of plants, which, though not so 

 thick as a hair, are yet more powerful than those of animals 

 that are thicker than the finger. 



After having made his experiments on the force of ascent 

 in the sap, Hales attempted to ascertain the rapidity with 

 which it moved. In order to attain this end, he hollowed 

 out a deep hole in the soil, laid bare a small root of a tree, 

 introduced it into a tube filled with water, and plunged the 

 tube into mercury. To his great astonishment he very soon 

 perceived that the metal rose in the tube half an inch per 

 minute. 



We repeat this experiment in our amphitheatre every 

 year in presence of our pupils, but not being able to try it 

 there on a tree planted in the soil, we are forced to take an- 

 other method than that adopted by the Canon of Windsor. 

 We simply take a strong branch of a tree, which is care- 

 fully fitted into a large tube filled with water (see Fig. 178). 

 From this proceeds a long narrow tube, the end of which is 

 plunged into a vessel containing water colored with either 

 carmine or indigo. When the apparatus is properly fitted, 



