Minnesota Plant Life. 



251 



the second season. In the scarlet oak the foliage turns scarlet 

 red in autumn, while in the black oak the leaves turn brown. 

 In this way the three related species may be distinguished. In 

 some instances, it should be mentioned, the inner bark of the 

 scarlet oak is red rather than gray. The other Minnesota oaks 

 mature their acorns in the autumn of the first year. Of these 

 the white oak is distinguished by its deeply lobed leaves and 

 shallow cups, while the bur-oak has the cup deep and com- 

 posed of scales which form a bur-like growth different from the 

 smooth hard cup of the white oak. In the remaining native 

 oaks the leaves are notched 

 but are not lobed in the char- 

 acteristic oak fashion, and in 

 both of them the acorns are 

 sessile on the branches. The 

 chestnut-oak is a tall tree with 

 grey bark and has a chestnut- 

 like aspect. The scrub chest- 

 nut-oak is a shrub with the 

 leaves considerably broader 

 than in the chestnut-oak 

 proper. 



Some of the oaks, notably 

 the black oak, cling to their 

 leaves for a long time after the 

 frosts have killed them, some- 

 times even throughout the 

 winter. This habit is possibly 



the indication of an original southern range for the black oak 

 and a late extension of its range to the north, so that it has not 

 fully learned how to cut its leaves from the twigs as the other 

 more northern varieties are able to do. The bur-oaks in Min- 

 nesota, together with the black oaks, form oak-barrens. These 

 wastes, covered with grotesquely branching trunks, form pic- 

 turesque forests in the central part of the state. 



The ninth order includes three families, the elms with the 

 hackberries, mulberries and Osage oranges; the India-rubber 

 trees, figs, hemps and hops, and the various kinds of nettles. 



FIG. 117. American elm. After Britton and 

 Brown. 



