RESIN PASSAGES 



J 49 



with the single exception of Taxus, have resin passages or resin 

 reservoirs, which vary in distribution and number according 

 to the species." This statement would include the leaves and 

 bark, and sometimes even the pith of species which produce 

 neither isolated resin cells nor resin reservoirs of any kind in 

 the xylem tissue of the stem. It directs attention somewhat 

 forcibly to the fact that while the occurrence of resin reservoirs 

 in the fundamental tissue is a legitimate inheritance of the 

 mucilage canals of the Eusporangiate ferns and the Cycado- 

 filices, as also later of the resin cells of Cordaitales, the xylem 

 structure is the very last to receive the impress of such a course 

 of development ; and it is therefore in nowise surprising that 

 the resin passages do not appear there until a very late period 

 of development, and that their organization can even then be 

 brought about only through a somewhat prolonged series of 

 changes which are initiated by the occurrence of isolated resin 

 cells, much as the formation of mucilage canals may be traced 

 back to specialized cells which separately have the same func- 

 tion in the Eusporangiate ferns. 



The local occurrence of resin passages in the xylem of the 

 floral axis in no way invalidates the obvious 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 (62, 35), that "Those genera which 

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

 growth later produce single parenchyma 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 



