214 PROCESS OF DEVELOPEMENT. C#AP, IV. 



which the pith is supposed to be also peculiarly 

 destined to give origin to the future buds. 

 Origin and The next topic of inquiry is that of the genera- 

 of the a tion of the layer of wood in our example of woody 

 layers or pl ants > or of the parts analogous to wood in the case 

 otherwise. o f herbaceous plants ; a topic that has been hitherto 

 but little attended to. Phytologists have indeed of- 

 fered many conjectures concerning the origin of the 

 annual layer that is added to perennials; but they do 

 not seem to have taken up the subject at the proper 

 point. They have generally made their observations 

 on trees of considerable age and magnitude, a.nd have 

 contended, some that the wood is formed from the pith,, 

 others that it is formed from the bark, and others 

 that it is formed from the alburnum of the former 

 year ; thus evading the subject of the formation of 

 the original layer altogether, which is the foundation 

 of all the rest, and the most essential step in the 

 process of vegetation ; though it is a step concern- 

 ing which there can be but little said that is at all 

 satisfactory. If we suppose the rudiments of all 

 the different parts to exist already in the embryo, 

 then we have only to account for their developement 

 by means of the intro-susception and assimilation 

 of sap and proper juice; but if we suppose them 

 to be generated in the course of vegetation, then the 

 difficulty of the case is augmented : and at the best 

 we can only state the result of operations that have 

 been so long continued as to present an effect cog- 



