AND FORMATION OF ROOTS. 155 



obstruction of the ascending sap. The roots which are emitted in the 

 preceding case do not appear in any degree to differ from those which 

 descend from the radicles of generating seeds, and both apparently 

 derive their matter from the fluid which descends through the cortical 

 vessels. 



There are several varieties of the apple-tree, the trunks and branches 

 of which are almost covered with rough excrescences, formed by con- 

 geries of points which would have become roots under favourable circum- 

 stances; 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 around, 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 \vas 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 experiments ; not 

 that I supposed, or now suppose, that roots can be changed into buds, or 

 buds into roots ; but I had before proved that the organisation of the 

 alburnum is better calculated to carry the sap it contains, from the root 

 upward, than in any other direction, and I concluded that the sap when 

 arrived at the top of the cutting through the alburnum would be there 

 employed, as I had observed in many similar cases, in generating buds, and 

 that these buds would be protruded where the bark was young and thin, 

 and consequently afforded little resistance *. I had also proved the bark 

 to be better calculated to carry the sap towards the roots than in the 

 opposite direction, and I thence inferred that as soon as any buds, 

 emitted by the cuttings, afforded leaves, the sap would be conveyed from 

 these to the lower extremity of the cuttings by the cortical vessels, and 

 be there employed in the formation of roots f. 



Both the alburnum and bark of trees evidently contain their true sap ; 



* See above, No. VI. 



