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 in 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, caudicibits seclia, mirahile dictu, 

 IS'vdihir e sicco radix oleagina ligno." ' Georg.' Bk. ii. 



I have seen many specimens of adventitious roots 

 produced on the ohve 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 a laburnum stem. In the same 

 journal, January 1st, 1853, p. 4, Mr. Booth mentions 

 the case of a Cornish elm, the tnmk 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 familiar 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 



