NOTES. 



233 



generated by cellular tissue, they also belong to the horizontal 

 system ; and hence it is that the stock will always produce 

 branches like itself, notwithstanding the long superposition of 

 new wood which has been taking place in it from the scion. 



" The case of a ring of red bark always forming red wood 

 beneath it, is precisely of the same nature. After the neyv 

 bark has adhered to the mouths of the medullary rays of the 

 stock, and so identified itself with the horizontal system, it is 

 gradually pushed outwards by the descent of woody matter 

 from above through it ; but, in giving way, it is constantly 

 generating red matter from its horizontal system, through which 

 the wood descends, and thus acquires a colour not properly 

 belonging to it. With regard to the instances of grafts over- 

 growing their stocks, or vice versd^ it seems that these are sus- 

 ceptible of explanation on the same principle. If the horizontal 

 system of both stock and scion has an equal power of lateral 

 extension, the diameter of each will remain the same ; but, if 

 one grows more rapidly than the other, the diameter will 

 necessarily be different : where the scion has a horizontal 

 system that developes more rapidly than that of the stock, the 

 latter will be the smaller, and vice versa. It is, however, to be 

 observed, that in these cases plants are in a morbid state, and 

 will not live for any considerable time. 



Another case was, that if a large ring of bark be taken from 

 the trunk of a vigorous elm or other tree, without being 

 replaced with anything, new beds of wood will be found in the 

 lower as well as the upper part of the trunk ; while no ligneous 

 production will appear on the ring of wood left exposed by the 

 removal of the bark. ISTow this is so directly at variance with 

 the observations of others, that it is impossible to receive it as 

 an objection until its truth shall have been demonstrated. It 

 is well known, that, if the least continuous portion of liber be 

 left upon the surface of a wound of this kind, that portion is 

 alone sufficient to establish the communication between the 



