J]8 ON THE ORIGIN AND FORMATION OF ROOTS. 



VIII. 



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

 T. A. Knight, Esq. F. R. S. to the Right Hon. Sir Jo- 

 seph Banks, /i. B. P. R. S*. 



My dear Sir, 



Butis of trees AN my former communication I have given an account of 



spring frcm some experiments, which induced me to conclude, that the 

 the alburnum. , , ,. . . , , „ , • ,, 



buds or trees invariably spring irom their alburnum, to 



which they are always connected by central ves.els of 

 greater or less length; and in the course of much subse- 

 quent experience I have not found any reason, to change 

 the opinion tiiat I have there giveat* f^e object of the 

 present communication is to* show, that the roots of trees 

 are always geiierated by the vessels which pass from the co- 

 tyledons of the seed, and from tlie .eaves, through the leaf- 

 stalks and the bark, and that they never, under any circum- 

 stances, spring immediately from the alburimm. 

 The radicle in The organ, which naturalists have called the radicle in 

 the seed not the seed, is generally supposed to be analogous to the root 

 thp root. «,,,.! ,. . • 



of the plant, and to become a perfect root during germina- 

 tion; and I do not know that this opinion has ever been 

 controverted, though I believe, that, when closely investi- 

 gated. It will prove to be founded in errour. 

 Hoot lengthen A root, in all cases with which I am acquainted, elon- 

 by ue V parts gates only by new' parts, which are successively added to its 

 oiuto apex or point, and never, like the stem or branch, by the 



extension of parts previously organized ; and I have endea- 

 voured to show, in a former memoir, that, owing to this dif- 

 ference in the mode of the growth of the root and length- 

 ened plumule of germinating seeds, the one must ever be 

 obedient to gravitation, and points towards the centre of 

 the Earth, while the other must take the opposite direction^. 

 Radicle of But the radicle of germinating seeds elongates by the ex- 



* From the Philos. Tran .ict. for 1809, p. 1G9. 

 + Piiil. Trans. 18G5; Journal, vol. Xill, p. CAO. 

 % Phil. Tians. 1806 5 Journal, vol. XiV, p. 4 . 



tension 



