156 ON THE ORIGIN 



but whether the fluid which ascends in such cases as the preceding through 

 the alburnum, to generate buds, be essentially different 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 particles which are endued with life ; were I to offer 

 a conjecture, I am much more disposed to believe that the same fluid, 

 even by merely acquiring different motions, may generate different organs, 

 than that two distinct fluids are employed to form the root, and the bud 

 and leaf. 



When alburnum is formed in the root, that organ possesses, in common 

 with the stem and branches, the power of producing buds, and of emitting 

 fibrous roots ; and when it is detached from the tree, the buds always 

 spring near its upper end, and the roots near the opposite extremity, as 

 in the cuttings above mentioned. The alburnum of the root is also 

 similar to that of other parts of the tree, except that it is more porous, 

 probably owing to the presence of abundant moisture during the period 

 in which it is deposited*. And possibly the same cause may retain the 

 wood of the root permanently in the state of alburnum ; for I have shown, 

 in a former memoir, that if the mould be taken away, so that the parts of 

 the larger roots, which adjoin the trunk, be exposed to the air, such parts 

 are subsequently found to contain much heart wood*f . 



I would wish the preceding observations to be considered as extending 

 to trees only, and exclusive of the palm tribe : but I believe they are 

 nevertheless generally applicable to perennial herbaceous plants, and that 

 the buds and fibrous roots of these originate from substances which cor- 

 respond with the alburnum and bark of trees. It is obvious, that the 

 roots which bulbs emit in the spring, are generated by the sap which 

 descends from the bulb, when that retains its natural position ; and such 

 tuberous-rooted plants as the potato offer rather a seeming than a real 

 obstacle to the hypothesis I am endeavouring to establish. The buds of 

 these are generally formed beneath the soil ; but I have shown, in a 

 former memoir, that the buds on every part of the stem may be made to 

 generate tubers, which are similar to those usually formed beneath the 

 soil ; and I have subsequently seen, in many instances, such emitted by a 

 re-produced bud, without the calix of a blossom, which had failed to pro- 

 duce fruit ; but I have never, under any circumstances, been able to 

 obtain tubers from the fibrous roots of the plant. 



* See above, No. VI. for 1805. t Ibid. 



