222 THE ANATOMY OF WOODY PLANTS 



upward is clearly derived from transfusion tissue. This category 

 of tissue is the final stage of persistence of the protean centripetal 

 or cryptogamic wood of the lowest vascular plants. In the angio- 

 sperms the mechanical tissues in the walls of the anthers exemplify 

 the highest level of survival of the old centripetal wood of the 

 Pteridophyta and the lowest gymnosperms. In fact, the so- 

 called fiber layer of the anther in the case of the angiosperms 

 supplies the clearest instance of the persistence of this ancestral 

 structure outside of that most conservative of all organs, the root, 

 in which, as has been made clear in an earlier chapter, it still 

 maintains its pristine development in the primary organization. 

 The two mechanisms correlated with sporangial dehiscence pre- 

 viously described may appropriately be designated as ectokinetic 

 and endokinetic. 



