PAPERS ON BIOLOGY AND AGRICULTURE 91 



12. Gymnocladus dioica (coffee tree) — Mycorrhizas 

 lacking. Ultimate branches coarse. Growing tips whitish 

 but soon becoming brown. Thick-walled root hairs present 

 but not abundant. Bark dark tan when scraped. 



13. Juglaiis nigra (walnut) and J. cinerea (butternut) 

 — Mycorrhizas ordinarily lacking. Ultimate branches in- 

 termediate in size. Growing tips rather dark gray. Roots 

 when broken or crushed having a distinct odor of walnuts. 

 Bark yellow when scraped. 



14. Morns cdba (white mulberiy) — Mycorrhizas lack- 

 ing. Ultimate branches fine. Growing tips yellowish. Bark 

 yellow to orange when scraped. 



15. Asimina triloba (pawpaw) — Mycorrhizas lacking. 

 Ultimate branches very coarse. Growing tips dark brown. 

 Bark black when scraped. 



16. Benzoin melissae folium (spice bush) — Mycorrhizas 

 lacking. Ultimate branches coarse. Growing tips light 

 brown. Bark dark brown when scraped. 



The spice bush never becomes a tree but it is included 

 here because it occurs very abundantly along with the trees 

 considered. 



17. Fraxinus americana (white ash) and F. quadrangu- 

 lata (blue ash) — Mycorrhizas lacking. Ultimate branches 

 coarse. Growing tips dull white. Bark creamy white when 

 scraped. 



