98 



UPWARD GROWTH OF THE HEAD, AXD pt. ii. 



measurement. Indeed, I marvel why tap-rootists do 

 not pluck all their oaks like radishes or carrots, instead 

 of, according to their doctrine, cutting them exactly in 

 twain and leaving their lower halves to rot in the earth. 

 But let any one in any soil dig a trench six feet deep 

 close round an oak ; he will soon give up the idea of a 

 tap-root. 



Magnis componere parva, in the beginning of April, 

 1846, I planted a horse-chestnut on a column of earth 

 about 7 ft. high, formed by placing three chimney-pots 

 one on the other. In the autumns of 1850, 1851, 

 1852, 1853, and 1854, I knocked off each year about 

 a foot of the upper part of the chimney-pots, and 

 denuded the roots to that extent : they are, however, 

 branching. The ends of the branches, on reaching the 

 sides, had apparently died, and new shoots from them 

 had struck downward. There was not the least 

 circular growth round the sides, as with plants in 

 flower-pots ; possibly, because the chimney-pots were 

 encrusted with soot. Two of the upper roots were 

 entirely cleared from the earth in 1850. The woody 

 parts of them are still alive (1853), though it would 

 puzzle us to say whence their wood is supplied with 

 sap : I suppose, from the stem ; if so, the upward sap, 

 in this case, is a downward sap. 



The ' herbaceous envelope ' of these roots (that is, 

 the surfa.ce of the bark immediately below the outer 

 bark) is perfectly green where they are exposed to 

 light and air, and perfectly white from the very spot 



