DICOTYLEDONOUS (EXOGENOUS) STEMS. 67 



The formation of thick cellular rings at the edges of the decor- 

 tications was alluded to : these were especially conspicuous in 

 the Elm. The young parenchym of the bark, exposed on its 

 horizontal section in order to remove a ring, appeared to take 

 part in this formation, and enjoying, in the case of the upper 

 edge of the annulus, an abundant supply of elaborated sap, the 

 multiplication of cells became active, rapid, and irregular. 



The conclusions which we considered ourselves legitimately 

 entitled to adduce were embodied in a paragraph of the paper 

 read before the Club, which I subjoin. 



" Having ascertained then, as A. Trecul had previously done, 

 that when the surface of a Dicotyledonous Tree is laid bare by 

 decortication, the cells thus exposed, if protected sufficiently 

 from the influence of the weather, can reproduce layers of tissue — 

 that these reproduced plates may be formed without any direct 

 vertical connection with either bark, buds, or leaves above — that 

 these plates are formed of cells developing and multiplying, we 

 have no reason to doubt, according to the usual laws, and that 

 no special series or kind of cells alone give rise to these forma- 

 tions, but that all appear indiflerently to take part — we may 

 conclude that the evidence rendered by this inquiry disproves 

 the theory of Radicular Fibres as applied to the formation of the 

 ligneous plates of a Dicotyledonous Stem, and that plates of tissue 

 formed on decorticated stems, are not prolongations of the cellu- 

 lar medullary plates merely, but may result immediately from 

 any exposed cells." 



.Finally, it may appear that undue importance has been attach- 

 ed by Trecul and by us to the Theory of Descending Radicular 

 Fibres of Du Petit Thenars and Gaudichaud.'^ I am willing to 

 admit that in a limited sense this may be the case ; yet I appre- 

 hend that these inquiries into the anatomical conditions of wood 

 increment may have assisted in placing in a clearer light the 

 true relations subsisting between the woody layers and the leaves 

 above, leaving no material basis for such supposition, while at 

 the same time the recent statements of the latter author as to the 



♦ Perhaps Schleiden (Principles, p. 257) speaks rather too dogmatically upon this 

 subject. See, on the other hand, Schacht, "Die Pflanzenzcllc" p. 175. 



