)22 ^^ ''^"^ OaiGIN AND FORMATION OF ROOTS. 



possibly tile same cause may retain the wood of the root 

 permanently in the state of all)urnum; 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 ex- 

 posed to the air, such parts are subsequently found to con- 

 tain much heart wood*. 

 Buds and I would vvish the [)recedin(i- observations to be considered 



*eJenni'Th'e °/ ■'^'' extending to trees only, and exclusive of the palm tribe ; 

 baceous plants but I believe they are nevertheless generally a|)plicable to 



yttxluced from perennial herbaceous plants, and that the buds and fibrous 



suDstiinces cor- . . „ 



responding to I'oots of these originate from substances which correspond 



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

 and bark, , i • i i n • • i i . 



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



the sap, which de-cends from the bulb when this retains its 

 natural position ; and such tuberous rooted plants as the po- 

 tato offer rather a seeming than a, real obstacle to the hypo- 

 thesis 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 usu- 

 ally formed beneath the soil ; and I have subsequently seen, 

 in many instances, such emitted by a reproduced bud with- 

 out the calyx of a blossom, which had failed to produce 

 fruit; but 1 have never, under any circumstances, been 

 able to obtain tubers from the fibrous roots of the plant. 

 The tuber lit- The tuber therefore appears to diHer very little from a 

 from'a bmncb branch, which has dilated instead of extending itself, except 

 that it becomes capable of retaining life during a longer, 

 period; and when I have laboured through a whole sum- 

 mer to counteract the natural habits of the plant, a profu- 

 sion of blossoms has in many instances sprung from the 

 buds of a tuber. 

 and runners of The runners also, which, according to the natural habit of 

 tuberous root- the plant, give existence to the tubers beneath the soil, are 



ed pbnts simi- .... .. , r«ii 



lar in oin^i- very similar in organization to the stem of the plant, and. 



nzationto tbe j-eadily emit leaves and become converted into perfect stems, 



in a few-days, if the current of ascending sap be diverted 



into them ; and the mode in which the tuber is formed above 



and beneath the soil is precisely the same. And when the 



* Phil. Trans, for 1801. 



•HP, 



