[ 31 j 



V. On the Origin and Formation of Roots. In a Letter 

 fromT. A. Knight, Esq., F.R.S., to the Right Hon. 

 -Sir Joseph Banks, K.B., P.R.S.* 



MY DEAR SIR, 



In a former communication T have given an account of 

 some experm)ents, which induced me to conclude that the 

 buds of trees invariably spring from their alburnum, to which 

 they are always connected by central vessels of greater or 

 less length ; and in the course of much subsequent expe- 

 rience, I have not found any reason to change the opiniou 

 that I have there given f. The object of the present com- 

 munication is to show, that the roots of trees are always ge- 

 nerated by the vessels which pass from the cotyledons of the 

 seed, and from the leaves, through the leaf-stalks and the 

 bark, and that they never, under any circumstances, spring 

 immediately from the alburnum. 



The organ, which naturalists have called the radicle in the 

 seed, is generally supposed to be analogous to the root of the 

 plant, and to become a perfect root durinij germination; ard 

 1 do not know that this opinion has ever been controverted 

 though I believe that, when closely investigated, it will prow 

 to be founded in error. 



A root, in all cases with which I am acquainted, elongates 

 only by new parts which are successively added to its apex or 

 point, and never, like the stem or branch, bv the extension 

 ofparts previously organized; and I have endeavoured to 

 show, in a former memoir, that owing to this diflercuce ia 

 the mode of the growth of the root and lengthened plumule 

 of germinating seeds, the one must ever be obedient to gra- 

 vitation, and point towards the centre of the earth, whilst 

 the other must take the opposite direction J. But the radicle 

 of germinating seeds elongates by the extension ofparts pre- 

 viously organized, and in a great number of cases, wliich 

 must be familiar to every person's observation, raises the 

 tolyledons out of the mould in which the seed is placed to 



• From Philosophical Transnctions for 1809, Part I. 



* Phil. Tram. 1«05. ^ It/iJ. iSOC. 



vegetate. 



