214 
 § 224. Oaks of the United States—In § 105, we gave some ac- 
count of Dr. Engelmann’s observations on this subject, read before 
the Academy of Science of St. Louis, March 20, 1876. Last Octo- 
ber, he read a continuation of that paper, in which he corrects some 
errors into. which he had fallen in the study of this very extensive, 
perplexing, but most interesting genus. We subjoin his revised ar- 
rangement of our Oaks. The names in parenthesis designate sub- 
species. — 
I. Lepidobalanus, Endl. 
A, LLEUCOBALANUS. 
* Maturatio annua, 
+ Folia decidua. © 
Q. alba, lobata (fruticosa), Garryana, stellata, macrocarpa, 
lyrata, bicolor ( Michauxti), Prinus, Muhlenbergit (pri- 
noides ), Douglasii, undulata (pungens ). 
+ + Folia persistentia. 
Q. oblongifolia, dumosa, reticulata, virens, 
; -: : - ** Maturatio biennis. neue 
Q. chrysolepis (vacciniifolia, Palmeri), tomentella. 3 
‘B. MELOBALANUS: Ovula abortiva (excepta Q. Zmory?) supera, 
-€tc., ut'In pag. Ior. 
. - * Maturatio annua, folia persistentia. 
QO. Emoryi, agrifolia, pumila, hypoleuca. 
>. ** Maturatio biennis. 
_ + Folia decidua. : 
Q. rubra, coccinea ( tinctoria), Sonomensis, falcata, Catesbaet, 
ilicifolia, palustris, Georgiana, aquatica, laurifolia, 
nigra, cinerea, imbricaria, Phellos. 
+t Folia persistentia, 
ee Q. Wislizent, myrtifolia. . , 
II. Androgyne, A. DC. 
Q. densiflora. 
-The collection of oak woods at the Centennial Exhibition fur- 
nished interesting facts. The Black-oaks grow, on an average, 
nearly twice as fast as the White-oaks. The heartwood of the 
latter is always readily distinguished, but of the Black-oaks is 
scarcely, if at all, darker than the sapwood. The Black-oaks of the 
present day are confined to America, principally to the Atlantic 
region, but in the tertiary period they extended into the old world. 
Occasionally Black-oaks are found with cup-scales thickened at 
base. Prof. Sargent has collected near Cambridge fruits of t/écéfolia 
with this peculiarity, and it does not seem to be rare at all in the 
northern forms of rubra, Q. Lmoryt, in the former part of the 
paper placed among the White-oaks, has basal ovules, but, being in 
every other respect a true Black-oak, has been placed in this section. 
Q. Muhlenbergii is the name given to what we used to call Q. 
castanea, Muhl., Q. Prinus acuminata, Mchx., which the Dr. is satis- 
, 
