424 The Rev. P. Keith on the Origin of Buds. 



plants which have their diameters augmented by the addition 

 of annual and concentric layers. It may include dicotyledonous 

 perennials ; but dicotyledonous annuals, and monocotyledonous 

 plants, as well as plants without cotyledons, it cannot possibly 

 apply to. 



It is admitted that buds, though not originating as above, 

 may be produced from any layer of alburnum by artificial 

 means ; — what are these means ? — but it is contended that Na- 

 ture never protrudes a branch-bud except in the aforesaid way. 

 At all events, the discovery is not entirely new. It is at least 

 as old as the researches of Mrs. Ibbetson, who saw, as I be- 

 lieve, through the medium of the microscope, the buds in the 

 very act of crossing the concentric layers on their way to the 

 alburnum, and who has advocated and illustrated the fact and 

 the doctrine with the most laudable zeal*. She thought, in- 

 deed, that the bud is originally formed in the root, from whence 

 it ascends by " the line of life" — that is, the medullary sheath — 

 till at last some unknown but potent and irresistible cause gives 

 it a horizontal direction, and forces it ultimately to the circum- 

 ference, in spite of all intervening layers of wood, however nu- 

 merous and however hard. This was indeed very difficult to 

 believe ; and was, as I should suppose, never much believed. 



But the subject was not left to be elucidated merely by the 

 labours of Mrs. Ibbetson. It had long occupied the attention 

 of M. Du Petit-Thouars, a French botanist distinguished for 

 his able Illustrations of the Plants of Madagascar. In a paper 

 entitled De la Terminaison des Plant es, and read at a sitting of 

 the Royal Academy of Sciences on the 7th of October, 1816, he 

 exhibits the result of his observations, and develops his views 

 at some length. The following extracts will show that the 

 doctrine of the central origin and horizontal protrusion of buds 



* Phil. Mag. vol. 45. 56. 



comes 



