S2 ON THE ALBURNUM OF TREES. 



posite directions, and as well through inverted cuttings as 

 others, is totally erroneousf. 

 The albumous If the sap be raised in the manner I have suggested, 

 tubes reservoirs much f j t w ^]| p ro bably accumulate in the alburnum in 

 the spring; because the powers of vegetable life are, at that 

 period, more active than at any other season; and the leaves 

 are not then prepared to throw off any part of it by transpi- 

 ration. And the cellular substance, being then tilled, may 

 discharge a part of its contents into the alburnous tubes, 

 which again become reservoirs, and are filled to a greater or 

 less height, in proportion to the vigour of the tree, and the 

 state of the soil and season: and if the tubes which are thus 

 filled be divided, the sap will flow out of them, and the tree 

 will be said to bleed. But as soon as the leaves are unfolded, 

 and begin to execute their office, the sap will be drawn from 

 its reservoirs, and the tree will cease to bleed, if wounded. 

 These tubes The alburnous tubes appear to answer another purpose in 



are analogous trees an( j to b e analogous, in some decree, in their effect*, 



to the cavities . . . , . '.. 



in bones, in- to the cavities in the bones of animals; by which any de- 



c 5 eas JJ 1 F • h gr.ee of strength, that is necessary, is given with less expen- 

 out weight, diture of materials, or the encumbrance of unnecessary 

 weight; and the wood of many different species of trees is 

 thus made, at the same time, very light, and very strong, the 

 rigid vegetable fibres being placed at greater distances from 

 each other by the intervention of alburnous tubes, and con- 

 sequently acting with greater mechanical advantage, than 

 they would if placed immediately in contact with each 

 other. 



The air in the J nave s hown in a former communication, that the specific 



alburnous „ . . . , . .-, 



tubes conduces gravity ot the sap increases during its ascent in the spring, 



to the produc- and that saccharine matter is generated, which did not pre- 



tion of sugar, v j ous iy. ex - gt j n ^ e alburnum, or in the sap, as it rose from 



the root: and I conceive it not to be improbable, that the 



air contained in the alburnous tubes may be instrumental in 



as when apples tne generation of this saccharine matter. For I discovered 



are ground to in the last autumn, that much air is absorbed, or at least 



m eci er, disappears, during the process of grinding apples for the 



purpose of making cider, and that during this absorption of 



• Phil. Trans, 1804, p. 5 j or Journal, vol. X, p. *9t. 



aic 



