SEAT OF VEGETABLE LIFE. 135 



tion of the last year's alburnum ; because that remains 

 precisely of the same form and dimension it had at 

 the end of the preceding- year. Neither has it sprung 

 from the liber ; because that also remains unchanged, 

 and is in fact superseded by the new one within it. 

 As then they are not parts of the members with 

 which they were and are in contact, they must either 

 be self-generated from the fluids of the system by the 

 assimilating powers of the plant, as has been by many 

 supposed, or from some vital member which has been 

 hitherto overlooked, or probably misnamed by physi- 

 ologists. 



That such organised matter as that of bark and 

 wood can be formed out of any possible accumulation 

 of gaseous, aqueous, gumrnous, or even resinous 

 fluids, or from their qualities, is extremely question- 

 able. We cannot conceive that the beautiful arrange- 

 ment of fibres, tubes, cells, and all the other structure 

 of the vegetable fabric can receive specific disposition 

 fortuitously. There must be a pre-existing organised 

 body whence such regular formations proceed. 



The beautiful forms and results of crystallisation 

 are indeed astonishingly admirable ; but they are 

 generated by chemical associations, and obey other 

 laws than those which govern vegetable development. 

 That chemical agency is present in all vegetable 

 processes is very probable, not, however, in such 

 potency as to create forms and vital substances, 

 farther than assisting the exhibition of them. 



It may be concluded, therefore, that the new layers 



