THE GYMXOSPERMAE : CONIFERALES AND TAXALES 671 



^ Cortex 

 Phloem 



Secondary xylem 



Primary xylem 

 Protoxylem 



Resin canal 



Fig. 669. — Finns sylvestris. Transverse section of j-oung 

 diarch root showing the primary xylem plate 

 separated from the secondary wood by a zone of 

 parenchymatous cells. A resin canal lies opposite 

 each protoxylem in the primary medullary rays. 



The younger roots of the Pine are commonly invested by fungal hyphae 

 which form a complete layer over the surface. This is called an ectotrophic 

 mycorrhiza. Great importance has been attached to this association in 

 regard to the nutrition of the tree (Fig. 670) (see Volume IV). 



Fig. 670. — Pitms sylvestris. Rootlets invested with mycor- 

 rhizal fungus, seen by dark-ground illumination. 



Anatomy of the Leaf. 



In a transverse section of the leaf we find a specialized structure different 

 from that obtaining either in the leaves of the Cr}'ptogams or in the typical 



