66 BETULACEAE 



^ to 11/2 inches in length on fruiting branchlets and nearly 2i/^ 

 inches in length on sterile branchlets. They are wedge shaped 

 at the base, more or less rounded, though occasionally acute, at 

 the apex, closely serrate on the margin, and at first hairy on 

 both surfaces but later glabrous or nearly so. The twigs, pu- 

 bescent when young, remain more or less so for a year or more 

 and become reddish brown or, later, somewhat grayish. 



The pistillate catkins are usually about 1/^ inch long and 14 

 inch wide and stand on stalks about 14 inch long. Their scales 

 are lobed to about the middle, the middle lobe being generally 

 the largest, the lateral ones more or less spreading and some- 

 what ciliate on the margin. The nutlets and the wings are 

 variable, the nutlets being ovate to slightly obovate and the 

 wings generally not so wide as the nutlets. 



Distribution. — The Dwarf Birch, a northern shrub, ranges 

 from Newfoundland to Saskatchewan and south to northern In- 

 diana and southeastern Minnesota. In Illinois, it occurs only in 

 the extreme northeastern corner of the state, in Cook and Lake 

 counties, in its typical habitat of bogs, swamps and lake shores. 



A variety, glandulifera Regel, is sometimes distinguished on 

 the basis that in glandulifera young twigs are more or less 

 abundantly dotted with glands. The typical form and this 

 variety may be found in the same habitat and are so likely to 

 intergrade that the distinction is made with considerable 

 difficulty. 



ALNUS B. Eberhart 

 The Alders 



The alders are shrubs or small trees, which bear alternate, 

 broad-bladed, toothed leaves and produce stalked but few-scaled, 

 solitary or raceme-like clusters of catkins. The pendulous stami- 

 nate catkins have 4 or 5 bractlets and 3 or 6 flowers clustered 

 at the base of each short-stalked scale, each flower having a 

 3- to 5-parted calyx and a similar number of stamens, the 

 anthers of which are 2 celled. The scales of the pistillate cat- 

 kins are fleshy and each covers 2 flowers and 2 small, adherent 

 scalelets. In fruit they are w^oody. 



The alders are shrubs of stream banks, riverbottoms and 

 swamps, as w^ell as of high mountainous regions. Of about 20 

 species, 9 are North American and 2 occur in Illinois. 



