ADVENTITIOUS ROOTS. 157 
considered to come within the scope of teratology, or, 
at least, where their production is the result of injury 
or of some unfavorable condition to which the plant 
is exposed. 
Thus the production of adventitious roots on the 
stem of the vine is considered to be due to untoward 
circumstances impairing the proper action of the ordi- 
nary subterranean roots. So, too, the formation of 
roots on the upper portions of stems that are more or 
less decayed below, as m old willows, is to be con- 
sidered as an attempt to obtain fresh supplies through 
a more vigorous and healthy channel. 
A similar occurrence often arises as a consequence 
of some injury. Virgil had this circumstance in view 
when he wrote 
“ Quin et, caudicibus sectis, mirabile dictu, 
Truditur e sicco radiz oleagina ligno.”— Georg.’ Bk. ii. 
I have seen many specimens of adventitious roots 
produced on the olive in the way just mentioned. 
In the ‘Gardeners’ Chronicle,’ January 8th, 1853, p. 
21, is described a curious formation of roots in the fissure 
between two divisions of alaburnum stem. In the same 
journal, January Ist, 1853, p. 4, Mr. Booth mentions 
the case of a Cornish elm, the trunk of which was 
divided at the top into two main divisions, and from 
the force of the wind or from some other cause the 
stem was split down for several feet below the fork. 
Around the edges of the fracture, layers of new bark 
were formed, from which numerous roots issued, 
some measuring an inch in diameter and descending 
into the cleft portion of the tree: similar instances 
must be familar to all observers. 
It may happen that these roots sent down into the 
cavity of a decaying trunk may, after a time, become 
completely concealed within it, by the gradual forma- 
tion and extension of new wood over the orifice of the 
cavity formed by the death and decay of the old wood. 
Such is presumed to be the explanation of a specimen of 
