134 



BUR OAK. 



Quercus macrocarpa, Michaux. 



FORM Usually attains height of about 70-80 feet but may reach a maximum height of 170 

 feet with a diameter of 6-7 feet. It attains its greatest height in Illinois and Indiana. It has 

 broad spreading branches which form a broad round-topped crown. In the forest the crown is 

 usually contracted and covers only the upper part of the trunk. It is a giant among its associ- 

 ates. 



BABE Intermediate between flaky bark of White Oak and very roughly ridged bark of 

 Chestnut Oak. 



TWIGS Stout, covered with pale, raised and inconspicuous lenticels, yellowish-brown, at first 

 hairy, later smooth, with corky wings often 1J inches wide. 



BUDS Alternate, broadly-ovate, about J of an inch long, acute or obtuse, reddish-brown, 

 slightly pubescent. Lateral buds are closely appressed. 



LEAVES Alternate, simple, 6-12 inches long, 3-6 inches wide, obovate or oblong; 5-7 lobed; 

 sinuses round-based; terminal lobe largest; smooth, shiny, and dark green above; paler and finely 

 hairy beneath. 



LEAF-SCARS See "Leaf -Scars" under White Oak, page 132. 



FLOWERS Mature about May. Staminate flowers borne in slender ament 4-6 inches long. 

 Pistillate sessile or short-stalked, with bright red stigmas and hairy scales. 



FRUIT An acorn, maturing during first season; sessile or stalked, usually solitary. Nut 

 ovate, 4/5 2 inches long, covered with down. Cup deep, embracing from i to entire nut, light 

 brown, downy on inner side, covered with large imbricated scales forming a distinct fringe near 

 the margin. 



WOOD Ring-porous; with conspicuous medullary rays; heavy, hard, strong, close-grained, 

 very durable, brownish with light thin sapwood. Weighs 46.45 Ibs. per cubic foot. Used for the 

 same purposes as White Oak from which it is not distinguished on the market. 



DISTINGUISHING CHARACTERISTICS In summer the Bur Oak, also known as Over-cup or 

 Mossy-cup Oak, can be distinguished by its unique leaves, which have deep, rounded sinuses 

 that reach almost to the midrib and divide each side of a leaf almost into two parts. The lobes 

 on the front part are rather squarish and those on the basal part triangular. The pubescence 

 on the lower side of the leaves and the corky winged projections on the branches are also 

 characteristic. In winter the corky winged projections on the branches, the closely appressed and 

 pubescent buds, the distinctly fringed acorn cups, and the persistent leaves are characteristic. 



RANGE Nova Scotia to Manitoba, south to Pennsylvania, Kansas and Texas. 



DISTRIBUTION IN PENNSYLVANIA Rare or local in the eastern, southern, and western 

 parts of the State. Not reported from other parts. 



HABITAT Prefers low rich bottomlands but can grow upon a variety of soils. It does not 

 thrive on uplands so well as the White Oak, grows much slower than the Red Oak, and is rather 

 intolerant of shade. 



IMPORTANCE OF THE SPECIES It is one of the very largest of American Oaks, has a wide 

 distribution, and occurs in pure and in mixed stands. This species produces valuable wood 

 especially adapted to quarter-sawing on account of conspicuous medullary rays. It should be re- 

 generated especially in the Mississippi basin where it develops at its optimum. This tree is also 

 very attractive as an ornamental or shade tree, since it withstands smoke more than most other 

 Oaks, and Is relatively free from disease. 



