134 LA HIRE'S THEORY. 



Grew, an English botanist, a contemporary of Newton, 

 and his fellow-member in the Royal Society of London, 

 attributed the rise of the sap to the play of the utricles 01 

 which the plant is composed. These utricles, he said, main- 

 tain a close intercommunication ; through their contraction, 

 the sap passes from the lower to the upper, and thus arrives 

 almost at the top of the plant. Grew's authority carried con- 

 viction to the minds of many botanists, particularly to those of 

 his compatriots. Yet was his opinion altogether imaginary ; 

 the supposed contraction of the utricles does not exist. 



La Hire, a French botanist, who flourished at the begin- 

 ning of the eighteenth century, son of the geometrician of 

 the same name, pretended that he could account for the 

 rise of the sap by the play of the little valves with which 

 the interior of the sap-vessels was furnished; at the same 

 time he assigned a very active rdle to the fibres of the 

 roots. The fibres elevate, he said, the whole column of 

 superimposed liquid, incessantly introducing, by a kind of 

 suction, new fluids into the organs. 



Unfortunately, the "play of the little valves, with which 

 the interior of the sap-vessels is furnished," is a pure inven- 

 tion of La Hire's. Instead of growing wise by experiment, 

 he suffered himself to be led astray by a false analogy. 

 Valves are found in the veins of man and the mammals ; 

 but no one has ever seen the sides of the vessels of a 

 plant garnished with valves to induce a circulation of the 

 sap. 



