NATURAL HISTORY. 



827 



as usual, and in other respects the 

 foetus varied much less from the 

 natural structure, than in any for- 

 mer instance. 



In the cases already on record, 

 we have seen that wherever the size 

 of the monster was mentioned, it 

 was much smaller than a natural foe- 

 tus. This would have led to the 

 supposition, that acirculation, which 

 was carried on by the action of the 

 vessels only, was incapable of main- 

 tainingthenaturalgrowth of a child, 

 had it not been found that the foe- 

 tus, which I have described, though 

 the heart was wanting, was fully 

 equal in size to a foetus of the same 

 age, which was possessed of that 

 organ. 



It may be observed, that in all 

 these cases, in which the heart was 

 wanting, the liver was wanting also. 

 It is probable that the action of 

 the vessels only, without the as- 

 sistance of the heart, would have 

 been insufficient to propel the blood 

 through the circulation of the liver, 

 which is so extensive in the natural 

 foetus 



On the Origin and Formation of 

 Roots. By T. A. Knight, Esq. 

 F.R.S. [^F7-om the same."] 



In a former communication I 

 have given an account of some ex- 

 periments, which induced me to 

 conclude that the buds of trees in- 

 variably spring from their albur- 

 num, to which they are always 

 connected by central vessels of 

 greater or less length ; and in the 



course of much subsequent experi- 

 ence, I have not found any reason 

 to change the opinion that I have 

 there given.* The object of the 

 present communication is to show, 

 that the roots of trees are always 

 generated by the vessels which pass 

 from the cotyledons of the seed, 

 and from the leaves, through the 

 leave-stalks and the bark, and that 

 they never, under any circum- 

 stances, spring immediately from 

 the alburnum. 



The organ which naturalists have 

 called the radicle in the seed, is ge- 

 nerally supposed to be analogous, 

 to the root of the plant, and to be- 

 come a perfect root during germi- 

 nation ; and I do not know that this 

 opinion has ever been controverted, 

 though I believe that, when closely 

 investigated, it will prove 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, by 

 the extension of parts previously 

 organized ; and I have endeavour- 

 ed to show in a former memoir 

 that owing to this difference in thf 

 mode of the growth of the root and 

 lengthened plumule of germinating 

 seeds, the one must ever be obedi- 

 ent to gravitation, and point to- 

 wards the center of the earth, whilst 

 the other must take the oppo- 

 site direction.! But the radicle of 

 germinating seeds elongates by the 

 extension of parts previously organ- 

 ized, and in a great number of 

 cases, which must be familiar to 

 every person's observation, raises 



the 



Vhil. Trans, for 1805. 



t PhiL Trans, for 1806. 



