272 



GYMNOSPERMS 



ditTcrcntiatcs. As the regions difTcrcntiate, it is evident that there is 

 an extensive, many-layered pericycle and a definite, one-layered 

 endodermis (fig. 272). Often there is a resin duct opposite each pro- 





Fig. 278. — Abies balsamea: transverse section of root, showing diarch primary xylcm 

 with a resin duct in the meta.xylem. The rays in the secondary wood show the sym- 

 metrical growth curves; X icx3. 



toxylem point; but sometimes there is a resin duct in the mctaxylcm, 

 as in Abies (fig. 278). 



The later stages in the structure of the root are much like those 

 in the stem, except that the tracheids are sometimes longer and 

 broader, and the growth-rings usually not so wide. 



