Betulaceae. 



25 



Alnus. Alder. 

 (Family Betulaceae). 



Typically shrubs: deciduous. 

 Bark smoky or gray, smooth or 

 fissured in rather large or scaly 

 areas. Twigs often 3-sided: pith 

 small, 3-sided, continuous. Buds 

 rather large, solitary, usually 

 stalked, with 3 subvalvate scales. 

 Leaf-scars alternate, half-round, 

 somewhat raised: bundle-traces 

 3, or the lowest compound: sti- 

 pule-scars narrow. 



Alders are particularly interest- 

 ing in winter through having 

 their buds distinctly stalked. 

 Though this character is by no 

 means limited to them, nor do 

 they all show it, there are few 

 genera in which it is so readily 

 observable. Their fruit is also 

 persistent in the form of small 

 cone-like bodies, which differ in 

 shape and position in different species, and as a rule the 

 staminate catkins for the next season are conspicuous. 

 1. Buds stalked. 2. 



*Buds sessile: bushes. 5. 

 Very tree-like. (European alder). A. glutinosa. 



Bushy, even when large. 3. 



3. Bud-scales narrow and separated. (1). A. maritima. 

 Bud-scales valvate. 4. 



4. Fruiting cones erect. (Smooth alder). (2). A. rugosa. 

 Fruiting cones pendent. (Speckled alder). (3). A. incana. 



5. Twigs glabrescent. (Mountain alder). A. crispa. 

 Twigs hairy. (Downy alder). A. mollis. 



