832 



ANNUAL REGISTER, 1805. 



bark of the graft, induces me to 

 believe, that the descending iiuid 

 undergoes some further changes in 

 the bark, possibly by discharging 

 some of its component parts 

 through the pores described and 

 figured by Malpighi. 



1 also suspected, since my former 

 paper was written, that the young 

 bark, in common with the leal, pos- 

 sessed a power in proportion to the 

 surface it exposes to the air and 

 liglit of preparing the sap to gene- 

 rate new wood ; for 1 found that a 

 Tery minute quantity of wood was 

 deposited by the bark, where it had 

 not any a})parcnt connection with 

 the leaves. Having made two in- 

 cisions through the bark round 

 annual shoots of the apple-tree, I 

 entirely removed the bark between 

 the incisions, and I repeated the 

 same operation at a little distance 

 below, leaving a small portion of 

 bark unconnected with that above 

 and beneath it. By this bark, a 

 very minute quantity of wood in 

 many instances appeared to be ge- 

 nerated, at its lower extremity. 

 The buds in the insulated liark were 

 sometimes suffered to remain, and 

 in other instances were taken away ; 

 but these, unless they vegetated, did 

 not at all aflect the result of the ex- 

 periment. I could therefore ac- 

 count for the formation of Avood, 

 in this case, only by supposing the 

 bark to possess in some degree, in 

 common with the leaf, the power to 

 produce the necessary changes in 

 the descending sap; or (hat some 

 matter, originally derived from the 

 leaves, was previously deposited in 

 the bark : or that a portion of sap 

 had passed the narrow space above, 

 from which the bark had been re- 

 moved, through the wood. Repeat- 

 ing the experiment, I left a much 

 3 



greater length of bark between the 

 intersections; but no more wood 

 than in the former instances was 

 generated. I therefore concluded 

 that a small quantity of sap must 

 have found its way through the 

 wood, from the leaves above ; and 

 I found, that when the upper in- 

 cisions were made at ten or twelve 

 lines distance, instead of one or two, 

 and the bark between them, as ijj 

 the former experiments, was re- 

 moved, no wood was generated bj 

 the insulated bark. 



I shall conclude my paper with a 

 few remarks on the formation of 

 buds in tuberous root«xl plants 

 beneath the ground. They must, if 

 my theory be well founded, be 

 formed of matter which has de- 

 scended from the leaves through the 

 bark. 1 shall confine my observa- 

 tions to the potatoe. Having'- raised 

 some plants of this kind, in a situa- 

 tion well adapted to my pur|)ose, 

 I waited till the tubers were about 

 half grown ; and I then commenced 

 mvexpcrimentby carefully intersect- 

 ing, with a sharp knife, the runners 

 which connect the tubers with the • 

 parent plant, and immersing each 

 end of the runners, thus intersected, 

 in a decoction of log-wood. At the 

 end of twenty-four hours I ex- 

 amined (he state of the experiment ; 

 and I found that the decoction had 

 passed along the runners in each 

 direction ; but I could not discover 

 that it had enlered any of the vessels 

 of the pare it plant. This result I 

 had anticipated ; because I con- 

 cluded, that the matter by which 

 the growing tuber is fed must de- 

 scend from tlie leaves through the 

 bark ; and experience had long be- 

 fore taught me that the bark would 

 not absorb coloured infusions. 1 

 now endeavoured to trace the pro- 

 gress j 



