RESIN PASSAGES 



153 



potentialities assume a more or less definite form. From this it 

 may be assumed that the primary growth ring is a zone within 

 which sporadic characters are common, but it is only in the later 

 rings that the various anatomical characters become permanently 

 developed and properly express the normal features of structure 

 and development. 



The considerations dealt with here, as well as in previous 

 chapters, lead us to give renewed emphasis to a view which 

 has been expressed elsewhere, and which finds justification in 

 many ways, not only in the gymnosperms but in the Salicaceae 

 and in Catalpa among the angiosperms, to the effect that inas- 

 much as the physiological activity of the plant is directly asso- 

 ciated with and dependent upon conditions of internal structure, 

 variations in the internal anatomy are to be regarded as of 

 primary importance, and such changes are no doubt established 

 or may be established considerably in advance of corresponding 

 alterations in the external character of the vegetative or even 

 of the reproductive organs. From this point of view questions 

 of internal structure must always have precedence over those of 

 external morphology in questions of classification. 



