NATURAL HISTORY. 



829 



of wliicli are almost covered with 

 rough excrescences, formed by 

 congeries of points which would 

 have become roots under favourable 

 circumstances ; and such varieties 

 are always very readily propa- 

 gated 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 ap- 

 plied to, the stems of other trees of 

 the same age and variety, and in 

 every respectj 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 cir- 

 cumstances no roots, but numer- 

 ous 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 mention- 

 ed, having been divided into pieces 

 of ten inches long, were plant- 

 ed 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 sup- 

 pose, that roots can be changed 

 into buds, or buds into roots ; but 

 I had before proved that the orga- 

 nization of the alburnum is better 

 calculated to carry the sap it con- 



* Phil. Trans, for 1805. 



tains, from the root upwards, than 

 in any other direction, and I con- 

 cluded that the sap, when arrived 

 at the top of the cutting through 

 the alburnum, would be there em- 

 ployed, as I had observed in many 

 similar cases in generating buds, 

 and these buds would be pro- 

 truded where the bark was young 

 and thin, and consequently afford- 

 ed little resistance.* I had also 

 proved the bark to be better cal- 

 culated to carry the sap towards 

 the roots than in the opposite di- 

 rection, 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 ; but whether the fluid which 

 ascends in such cases as the pre- 

 ceding through the alburnum to 

 generate buds, be essentially dif- 

 ferent from that which descends 

 down the bark to generate roots, 

 it is, perhaps, impossible to decide. 

 As nature, however, appears in 

 the vegetable world to operate by 

 the simplest means ; and as the 

 vegetable sap, like the animal 

 blood, is probably filled with par- 

 ticles which are endued with life, 

 were I to offer a conjecture, I am 

 much more disposed to believe 

 that the same fluid, even by mere- 

 ly acquiring different motions, may 

 generate different organs, than 

 tiiat two distinct fluids are em- 

 ployed to form the root, and the 

 bud and leaf. 



When alburnum is forqjed in the 



root, 

 t Ibid. 



