172 Mr. Knight on the Origin and Formation of Roots. 
their matter from the fluid which descends through the corti- 
cal vessels. 
There are several varieties of the apple tree, the trunks and 
branches of which are almost covered with rough excres- 
cences, formed by congeries of points which would have be- 
come roots under favourable circumstances ; and such varieties 
are always very readily propagated by cuttings. Having 
thus obtained a considerable number of plants of one of these 
varieties, the excrescences began to form upon their stems 
when two years old, and mould being then applied to them 
in the spring, numerous roots were emitted into it early in the 
summer. The mould was at the same time raised round, 
and applied to, the stems of other trees of the same age and 
variety, and in every respect similar, except that the tops 
of the latter were cut off a short distance above the lowest 
excrescence, so that there were no buds or leaves from which 
sap could descend to generate or feed new roots ; and under 
these circumstances no roots, but numerous buds were emitted, 
and these buds all sprang from the spaces and points, which 
under different circumstances had afforded roots. The tops 
of the trees last mentioned, having been divided into pieces 
of ten inches long, were planted as cuttings, and roots were 
by these emitted from the lowest excrescences beneath the 
soil, and buds from the uppermost of those above it. 
I had anticipated the result of each of the preceding expe- 
riments ; not that I supposed, or now suppose, that roots can 
be changed into buds, or buds into roots ; but 1 had before 
proved that the organization of the alburnum is better calcu- 
lated to carry the sap it contains, from the root upwards, than 
in any other direction, and I concluded that the sap when 
