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. i nb. Similar 

 conditions are of 

 widespread occur- 

 rence, and the root 

 clearly furnishes 

 evidence as to the 



nature of primi- 

 tive organization 



FIG. ma and b. Transverse section of rays in stem 

 and root in Betula papyrifera. Explanation in text. 



