TREES AND SHRUBS 51 



I. OSTRYA. Scop. Hop Hornbeam 



A small tree; sterile flowers consisting of several stamens in 

 the axil or each bract; fertile f.owers a pair to each deciduous bract, 

 enclosed in a bractlet which in fruit becomes a closed, bladdery bag, 

 the involucres forming a kind of strobile resembling that of the hop. 



1. O. bailey. 



2. ALNUS Hill. Alder 



Shrubs or smal' trees with thin, toothed leaves; sterile cat- 

 kins with 4 or 5 bracelets and 3 flowers upon each scale; fertile 

 catkins ovoid or ellipsoid, the scales each subtending 2 flowers and 

 a group of 4 small scales, the latter being woody in fruit, wedge- 

 obovate. 



Leaves rounded to truncate at the base, some- 

 what lobed, ovate to broadly oblong; sta- 

 mens 4. 1. .4. tenuifolia. 



■Leaves usually cuneate or at least narrowed at 

 the base, seldom lobed, the younger ones 

 lanceolate, the older elliptic or oblong; sta- 

 mens 1 to 3. usually 2. 2. A. oblongifolia. 



