THE STEM OF VASCULAR PLANTS. 179 



new shoot, which springs from its apex, and which ought 

 to be considered as the development of a new germ. Let 

 us first follow the case where the germ is situated exactly 

 at the summit ; it is developed during a year, following 

 the same laws as that of wliich it seems the continuation. 

 The stem is found elongated by a body perfectly similar 

 to that of the preceding year ; and thus it goes on succes- 

 sively for an indefinite period. A young shoot, formed of 

 the organs above described, acquires, during its first year, 

 a certain thickness, determined by the thickness of the 

 woody and cortical cones : the second year, at the same 

 time that a new shoot springs from its summit, it forms 

 in that of the preceding year a new woody zone, which 

 is placed on the outside of the old one, and a new cor- 

 tical one, situated within the preceding one : these two 

 zones then are developed in the space situated between 

 the cortical and woody bodies. What is their origin t 

 Such is the delicate question which has occupied the 

 greater number of anatomists and physiologists ; for it 

 appertains to both these sciences. What we shall say 

 with regard to the increase in diameter of the stems of 

 Dicotyledons, is equally true with respect to their roots. 

 Du Petit-Thouars, impressed with what takes 

 place in the formation of the branches of Draccsfia, 

 (which we shall speak of under Endogenous Stems,) 

 applying, by analogy, his observation to all stems, and 

 partaking of the idea, which appears to us very just, 

 that the liber does not change into alburnum, has 

 proposed an opinion, as bold as it is ingenious, upon the 

 origin of the woody fibres; viz. that they are the pro- 

 longation from above, downwards, of the buds or germs 

 which are developed. Thus, if we revert to what I have 

 said of the elongation of stems by the formation of a new 

 shoot at their extremities, he supposes that, at the same 

 time that this new shoot is developed, the fibres which 



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