PAPERS ON BIOLOGY AND AGRICULTURE 89 



KEY 



A — Ectotrophic mycorrhizas abundant B. 



AA — Ectotrophic mycorrhizas infrequent or lacking D. 



B — Bark red Carya ovata 1. 



BB — Bark yellow Carpinus caroliniana 2. 



BB— Bark brown C. 



C — Mycorrhizas usually white — Quercus rubra and Q. muhlenbergii 3. 



CC — Mycorrhizas usually brown — Tilia americana 4. 



D — Ectotrophic mycorrhizas present E, 



DD — Ectotrophic mycorrhizas lacking G. 



E — Bark brown L'lmus americana 5. 



EE — Bark whitish Carva cordiformis 6. 



EEE— Bark yellowish F. 



F — Ultimate branches fine — Celtis occidentalis 7. 



FF — Ultimate branches coarse — Aesculus glabra 8. 



G^Endotrophic mycorrhizal beads present Acer — 9. 



GG — Endotrophic mycorrhizal beads lacking H. 



H — Stiff brown root hairs present I. 



HH. — Stiff bro-wn root hairs lacking K. 



I — Ultimate branches fine — Cercis canadensis 10. 



II — Ultimate branches coarse J. 



J— Root hairs numerous — Gleditsia triacanthos 11. 



J J — Root hairs not numerous — Gymnocladus dioica 12. 



K— Roots with odor of walnuts — Juglans 13. 



KK — Roots without odor of walnuts L. 



L — Ultimate branches fine — Morus alba 14. 



LL — Ultimate branches coarse M. 



M — Bark black — Asimina triloba 15. 



MM — Bark brown — Benzoin melissaefolium 16. 



MMM^Bark whitish Fraxinus IT. 



1. Carya ovata (shag-bark hickory) — Ectotrophic my- 

 corrhizas abundant, often yellow but sometimes white or 

 brown. Ultimate branches moderately fine. Growing tips 

 soon becoming brown. Bark distinctly red when scraped. 

 The general appearance of these roots is similar to that of 

 red oak and basswood but they are distinguished from the 

 latter by the red color of the bark. 



2. Carpinus caroliniana (blue beech) — Ectotrophic 

 mycorrhizas abundant, usually white. Ultimate branches 

 moderately fine. Growing tips soon brown. Bark yellow- 

 when scraped. Distinguished from oak, hickory and bass- 

 wood by the color of the bark. 



3. Quercus rubra (red oak) and muhlenbergii (yellow 

 or chestnut oak) — Ectotrophic mycorrhizas abundant, more 

 often white though sometimes brown. Ultimate branches 

 moderately fine. Growing tips soon becoming brown. Bark 

 distinctly brown when scraped. 



4. Tilia americana (basswood) — The roots of the bass- 

 wood very closely resemble those of the oaks. It is difficult 

 in most cases to distinguish them. The difference noted 

 in the key is that the mycorrhizas of basswood are more 



