THE ROOT 



155 



by fibers. The state of the ray figured for the root is the primi- 



tive one for the stem and the ancestral one for the genus Quercus, 



as evidenced by its 



tropical and sub- 



tropical represent- 



atives (live or 



evergreen oaks) 



which typically 



manifest the pres- 



ence of aggregate 



rays. In the genus 



Betula the same 



situation presents 



itself with refer- 



ence to the aggre- 



gate and diffuse 



rays. In the stem, 



as is shown in 



Fig . iiia, the 



multiseriate rays 



are diffused 



throughout the 



structure of the 



wood, while in the 



root aggregations 



of such rays are re- 



lated to the out- 



going traces of the 



secondary roots, 



Fig. ni&. Similar 



conditions are of 



widespread occur- 



rence, and the root 



clearly furnishes 



evidence as to the 



nature OI primi- 

 tive organization 



FIG. in a 



FlG 



FlG TIJ a and b Transverse section of rays in stem 

 and root in Betula papyri/era. Explanation in text. 



