90 ILLINOIS STATE ACADEMY OF SCIENCE 



often brown while those of the oaks are more often white 

 but it must be admitted that this is not a constant or de- 

 pendable difference. 



5. Ulmiis americana (American elm) — Ectotrophic 

 mycorrhizas present but usually not abundant, usually light 

 brown in color. Ultimate branches fine. Growing tips 

 whitish but soon becoming brown. Bark brown when 

 scraped. 



6. Carya cordiformis (pignut hickory) — Ectotrophic 

 mycorrhizas present but not abundant. Ultimate branches 

 intermediate in size. Growing tips creamy white. Bark 

 creamy white when scraped. 



7. Celtis occidentalis (hackberry) — Ectotrophic my- 

 corrhizas present but not abundant. Ultimate branches 

 very fine. Growing tips whitish, usually rather short. 

 Bark yellowish when scraped. 



8. Aesculus glabra (buckeye) — Ectotrophic mycorrhizas 

 present but not abundant. Ultimate branches very coarse. 

 Growing tips soon becoming gray. The older bark is easily 

 peeled off in flakes or layers, the outer layers being soft and 

 punky. Bark yellowish, sometimes tinged with pink. 



9. Acer saccharum (hard maple), A. saccharinum (sil- 

 vermaple) and A. rubrum (red maple) — Ectotrophic mycor- 

 rhizas lacking. Endotrophic mycorrhizal beads present, 

 usually more abundant and conspicuous in the soft maples 

 than in the hard maple. Ultimate branches intermediate 

 in size. Growing tips remaining whitish for some time. 

 Bark brown when scraped. 



10. Cercis canadensis (red bud) — Mycorrhizas lacking. 

 Ultimate branches fine. Growing tips whitish. Thick- 

 walled root hairs present but not abundant. Bark light tan 

 when scraped. 



11. Gleditsia triacanthos (honey locust) — Mycorrhizas 

 lacking. Ultimate branches coarse. Growing tips soon be- 

 coming brown. Thick-walled root hairs very abundant. 

 Bark light brown when scraped. 



