Chap. II.] 
COURSE OF THE SAP. 
83 
bleed from them alone; and it is, perhaps, pos¬ 
sible that the longitudinal upward flow of sap 
may be through these piths only, and the lateral 
flow through the silver grain, or medullary rays. 
But whether the central pith of the shoot of 
a pollard or coppice-wood stool originate in the 
wood of the stem, or of the last crop of branches, 
or in the supposed outside concentrical pith of 
one of these, should either or neither of these 
observations be correct, I think the case deserves 
investigation. I also think that such a question 
as this being hitherto unanswered —(might I not 
say, hitherto unasked f )—proves that we have yet 
much to learn in the science, and that there are 
many things under heaven and earth little 
dreamt of in our u physiology .” Unless these 
concentrical piths are piths, the growth of the 
bud, when disconnected from the central pith 
below it, disproves De Candolle’s ingenious sug¬ 
gestion, that the pith is the cotyledon of the bud: 
for the life of the seedling is dependent on its 
cotyledon,—that is, on its seed; and it perishes 
when disconnected from it, even after leaves are 
developed on the plant, and the roots are several 
inches long. But besides this, the cotyledon, or 
seed, is absorbed and vanishes in feeding the 
seedling, but the pith endures for ever. De 
G 2 
