OF THE WOOD. 29 



the alburnum and the wood are really the origin of the 

 new layers of wood, by producing first this gelatinous 

 substance, or matter of organization, which he and 

 Du Ilaniel call cambium^ and which Mirbel supposes 

 to produce the liber or young bark, and at the same 

 time, by a peculiar arrangement of the vascular parts, 

 the alburnum or new wood. His opinion is strength- 

 ened by the observation of a tribe of })lants to be ex- 

 plained hereafter, Palms, Grasses, &c. in wluch there 

 is no real bark, and in which he finds that the woody 

 fibres do actually produce the cambium. Dr. Hope's 

 experiment will scarcely invalidate this opinion, be- 

 cause it may be said the cambium had already in that 

 case formed the liber. 



This matter will be better understood when we 

 come to speak of Mw Knight's experiments on the 

 course of the sap. 



