VII. SCIENCE IX HER CELLS. 133 



11. However, 1 take tip first, and with best hope, Dr. 

 Asa Gray, who tells me (Art. 211) that pith consists of 

 parenchyma, ' which is at first gorged with sap,' hut that 

 many stems expand so rapidly that their pith is torn into 

 a mere lining or into horizontal plates; and that as the 

 stem grows older, the pith becomes dry and light, and is 

 i then of no farther use to the plant.' But of what use 

 it ever was, we are not informed ; and the Doctor makes 

 us his bow, so far as the professed article on pith goes ; 

 but, farther on, I find in his account of 4 Sap-wood,' (Art. 

 22i,) that in the germinating plantlet, the sap 'ascends 

 first through the parenchyma, especially through its cen- 

 tral portion or pith.' Whereby we are led back to our 

 old question, what sap is, and where it comes from, with 

 the now superadded question, whether the young pith is 

 a mere succulent sponge, or an active power, and con- 

 structive mechanism, nourished by the abundant sap : as 

 .Columella has it, 



"Natural! enim spiritu oinne alimentum virentis quasi 

 quaedam anima, per mediillain trunci veluti per sipho- 

 nem, trahitnr in summum." * 



As none of these authors make any mention of a com- 

 et rhubarb pith); but as rhubarb does not grow into wood, inappli- 

 cable to our present subject; and if we descend to annual plants, rush 

 pith is the thing to be examined. 



* I am too lazy now to translate, and shall trust to the chance of 

 some remnant, among my readers, of classical study, even in modern 

 England. 



