216 TREES OF MINNESOTA. 



The Black Oak class is characterized by leaves having 

 acute lobes and bristle-pointed teeth; acorns bitter, maturing 

 the second year, inner surface of shell of acorn woolly; wood 

 porous and brittle; roots spreading, seldom having clearly 

 defined tap roots except when young. 



Oak bark is used for tanning leather. The cork of com- 

 merce is the older bark of the Quercus suber of southern 

 Europe. Galls caused by insects puncturing the young and 

 tender shoots are produced on the branches of most oak trees 

 and are imported in large quantities from Asia Minor, China 

 and elsewhers to be used in the manufacture of inks and dyes. 

 The bark of most species is tonic and astringent and as a de- 

 coction is sometimes employed as an external remedy. 



Propagation. All the species grow readily from seeds 

 which have been kept properly, but if allowed to get dry they 

 are liable to lose their vitality. The seedlings have tap roots 

 often 3 to 4 feet long when the top is not more than a foot 

 high. On this account the trees are often very difficult and 

 uncertain to transplant, but if the tap roots are cut off a foot 

 from the surface of the ground when the trees are one year 

 old they form side roots and then may be moved with a 

 reasonable degree of certainty within the next few years be- 

 fore they have formed new tap roots. 



Quercus alba. White Oak. 



Leaves short petioled, oblong or obovate in outline, ob- 

 liquely cut into 3 to 9 oblong or linear and obtuse mostly en- 

 tire lobes, smooth excepting when young, pale or glaucous 

 underneath, bright green above, turning to a soft wine color 

 in autumn. Fruit an edible acorn maturing the first year, 

 hence borne on the shoot of the season, I to 1 inch long, ob- 

 long, often peduncled, not more than one-third covered by the 

 hemispherical saucer-shaped naked cup which is rough or 

 tubercled at maturity. A noble and picturesque tree some- 

 times attaining a height of 100 feet with a trunk 6 feet in 

 diameter but much smaller within our range. Its bark is 

 rough with longitudinal fissures and of a whitish gray color, 

 whence its name. It is also conspicuous from its holding 

 many of its dead withered leaves until nearly spring and in 



