III. THE LEAF. 47 



14. You know, in spring, and partly through all the 

 year, except in frost, a liquid called ' sap ' circulates in 

 trees, of which the nature, one should have thought, might 

 have been ascertained by mankind in the six thousand 

 years they have been cutting wood. Under the impres- 

 sion always that it had been ascertained, and that I could 

 at any time know all about it, I have put off till to-day, 

 19th October, 1869, when I am past fifty, the knowing 

 anything about it at all. But 1 will really endeavour now 

 to ascertain something, and take to my botanical books, 

 accordingly, in due order. 



(1) Dresser's " Rudiments of Botany." ' Sap ' not in 

 the index ; only Samara, and Sarcocarp, about neither 

 of which I feel the smallest curiosity. (2) Eiguiers 

 " Histoire des Plantes." * < Seve,' not in index ; only 

 Serpolet, and Sherardia arvensis, which also have no help 

 in them for me. (3) Bal four's " Manual of Botany." 

 'Sap, 3 yes, at last. "Article 257. Course of fluids in 

 exogenous stems." I don't care about the course just 

 now : I want to know where the fluids corne from. " If 

 a plant be plunged into a weak solution of acetate of 

 lead," I don't in the least want to know what happens. 

 " From the minuteness of the tissue, it is not easy to deter- 

 mine the vessels through which the sap moves." Who 

 said it was ? If it had been easy, I should have done it 

 myself. " Changes take place in the composition of the 



* An excellent book, nevertheless. 



