828 



ANNUAL REGISTER, 1809. 



the cotyledons out of the mould in 

 which the seed is placed to vege- 

 tate. The mode of growth of the 

 radicle is therefore similar to that 

 of the substance which occupies the 

 spaces between the buds, near the 

 point of the succulent annual shoot, 

 and totally different from that of 

 the proper root of the plant, which 

 I conceive to come first into exist- 

 ence during the germination of the 

 seed, and to spring from the point 

 of what is called the radicle. At 

 this period, neither the radicle nor 

 cotyledons contain any alburnum; 

 and therefore the first root cannot 

 originate from that substance ; but 

 the cortical vessels are then filled 

 with sap, and apparently in full ac- 

 tion, and through these the sap ap- 

 pears to descend, which gives exist- 

 ence to the true root- 

 When first emitted, the root con- 

 sists only of a cellular substance, 

 similar to that of the bark of other 

 parts of the future tree, and within 

 this the cortical vessels are subse- 

 quently generated in a circle, in- 

 closing within it a small portion of 

 the cellular substance, which forms 

 the pith or medulla of the root. 

 The cortical vessels soon enter on 

 their office of generating alburnous 

 matter ; and a transverse section of 

 the root then shows the alburnum 

 arranged in the form of wedges 

 round the medulla, as it is subse- 

 quently deposited on the central 

 vessels of the succulent annual 

 shoot, and on the surface of the al- 

 burnum of the stems and branches 

 of older trees.* 



If a leaf-stalk be deeply wound- 

 ed, a cellular substance, similar to 



that of the bark and young root, 

 is protruded from the upper lip of 

 the wound, but never from the 

 lower ; and the leaf-stalks of many 

 plants possess the power of emit- 

 ting roots, which power cannot 

 have resided in alburnum, for the 

 leaf-stalk does not contain any ; 

 but vessels, similar to those of the 

 bark and radicle, abound in it, and 

 apparently convey the returning 

 sap; and from these vessels, or per- 

 haps more properly from the Huid 

 they convey, the roots emitted by 

 the leaf-stalk derive their exist- 

 ence, j- 



If a portion of the bark of a 

 vine, or other tree, which read>ly 

 emits roots, be taken oil" in a circle 

 extending round its stem, so as to 

 intercept entirely the passage of 

 any fluid through the bark ; and 

 any body which contains much 

 moisture be applied, numerous 

 roots will soon be emitted into it, 

 immediately above the decorti- 

 cated space, but never immediately 

 beneath it ; and when the albur- 

 num in the decorticated spaces has 

 become lifeless to a considerable 

 depth, buds arc usually protruded 

 beneath, but never immediately 

 above it, apparenti}' owing to the 

 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 appa- 

 rently derive their matter from the 

 fluid which descends through the 

 cortical vessels. 



There are several varieties oftiic 

 apple-tree, the trunks and branches 



of 



• Phil. Trans, fur 1801. Plate 27. 



t riiU. Trans, for 1601. 



