702 



THE AMERICAN iXA TURALIST. [\'ol. XXXVIll. 



cell n 1 the formation of mucila-e c inals may he traced 

 back to specialized cells which separatel}- have the same function 

 in the Eusporangiate ferns. 



The local occurrence of resin passa^^^es in the xylem of the 

 floral axis in no way invalidates the ob\ ious conclusions to be 

 drawn from these statements, since it may be readily accounted 

 for in other ways. In a structure so unresponsive to influences 

 which would induce profound alterations as the xylem, it is to be 

 expected that important structural changes could be effected 

 only after a prolonged interval during which the fixation of any 

 particular character would be preceded by a period of sporadic 

 development within which such character would be liable to 

 recur under special conditions ; and as such conditions are obvi- 

 ously of fundamental importance we may inquire somewhat more 

 fully into their nature and results. 



The statement of Prantl (44. ]). 35) that "those genera 

 which are devoid of resin passages in the wood of young and 

 vigorous growth later produce single parench\ma elements in 

 the wood, which contain resin" requires some modification in 

 view of what Jeffrey has shown in the case of Sequoia and 

 Abies, as well as what has been shown in the course of the 

 present studies, and in its more comprehensive and exact form 

 it should read, " those genera which are usually devoid of resin 

 passages in the wood, hut some species of which may neverthe- 



produce single parenchyma elements in the wo;Kh which contain 



Taken by itself this statement as applied to Sequoia and 

 Abies might he held to indicate that the growth of the- first 

 year represents the most stable structural region of the entire 

 stem, in the sense that it embodies characters which are most 

 fully established, and that it will therefore embrace elements 

 which may he eliminated from the older parts, or which may be 

 •cplaced there by degenerate forms only. From this point of 

 view it would be necessary to regard the complex resin passage 



the primitive form of structure from which the cysts, groups 

 "t cells and is,,lated resin cells have been derived by a process 

 "t progressive degradation. This view appears to have been 



