82 MICHIGAN ACADEMY OF SCIENCE. 



ROUGH-BAKKED AND SMOOTH-BARKED WHITE OAKS. 



CHAS. A. DAVIS. 



The white oak, Querciis alba L., is described in most manuals of Botany 

 as a tree with light gray bark, scaling off in thin plates, and the writer 

 has always been accustomed to seeing it in such a form wherever he has 

 noted its occurrence. In examining trees of the species in the vicinity 

 of Ann Arbor, however, many specimens have been found in which a con- 

 siderable part of the boles was covered with the usual light-colored, scaly 

 and rather smooth bark, but upon other parts, spots of varying size 

 appear to be curiously and abnormally roughened. Such trees look as if 

 they had been scraped carefully except in the rough places, which are 

 often remarkably regular in outline. In the rough spots, the bark is 

 neither flaky nor light-colored, but is made up of firm, hard, high and 

 narrow ridges, of a dark color, with deep and regular clefts, which are 

 mainly longitudinal, but which frequently branch and are connected by 

 cross cracks and checks. More rarely the rough condition of the bark 

 is the one found upon the bole, while the flaky condition occurs in spots. 



The usual condition of the bark upon old bur oaks, Quercus macrocar- 

 pa Mx., in Michigan, is the rough, deply furrowed type, not flaky, but 

 with the ridges broader, w^th flatter tops and wider fissures than that 

 of the white oak, so that old specimens are among those having the 

 roughest bark of all our trees. Rather rareh- an individual is found in 

 which the bark is flaky and without ridges. In such cases the color is 

 much lighter than in the usual condition. 



A third type of white oaks, the chestnut oaks, Quercus acuminata 

 (Mx.) Houda, and Quercus Alexanderi Britton, occurs in the region 

 around Ann Arbor. The former is characterized by its thin, rather 

 smooth and flaky bark, while the latter has rough, heavily ridged bark. 

 Occasionally, specimens of the rough barked species occur with patches 

 upon which the bark is flaky, thin and relatively- smooth, so that it is 

 difficult to tell it from that of the thin barked species, except by other 

 characters. 



In all specimens of larger growth of Quercus platanoides (Lam.) 

 Sudw., which have been observed, the characters of the bark are those of 

 the bur oak, so far as the bole is concerned, and no special mention need 

 be made of this species farther than this. 



In all of these species, where the flaky, light-colored and thin bark 

 occurs, the bark is infested with a saprophytic, fungus, Corticium Oakesii 

 B. and C, Avhich seems to be the cause. of the separation of the layers and 

 the flaking which occurs. The mycelium of the fungus penetrates the 

 bark, dissolves out certain elements and leaves it in a spongy and por- 

 ous condition, and in this state the exfoliation and flaking which are so 

 characteristic in the bark of the white oak. go on, aided by the effects of 

 wind and weather, until the ridges, which would make the bark rough 

 are nearly or quite obliterated. 



The rather unusual dryness of many of the woodlots in southern 



