94 MIDDLESEX FLORA. 



COMPTONiA, Soland. 



C. asplenifolia, Ait. Sweet Fern. 

 Common. Apr. -May. 



BETULACE/E. BIRCH FAMILY. 



Betula, Touru. 



B. lenta, L. Cherry Birch. Sweet or Black Birch. 



Widely distributed. Frequent. Apr.-May. 



B. lutea, Michx, f. Yellow Birch. 

 Not as common as the preceding species. Apr.-May. 



B. alba, L. vr r. populifolia, Spach. American White Birch. 

 Gray Birch. 

 Common. May. 



B. papyracea, Ait. White Birch. Paper or Canoe Birch. 

 Rare eastward, but common in other sections of the county. May- 

 June. 



B. papyracea, Ait., var. minor, Tuclierm. Dwarf Canoe Birch. 

 A clump of trees 6 or 7 feet high, growing in a swamp in Lexing- 

 ton, 1875 (Minot Pratt) . 



B. nigra, L. River Birch. Red Birch. 

 Native only in the Merrimac River ValleJ^ 



Alnus, Tourn. 



A. incana, Willd. Black Alder. Speckled or Hoary Alder. 



Common. Mch.-Apr. 

 A. serrulata, Willd. Smooth Alder. 



Less common than the preceding species. Mch.-Apr. 



SALlCACEyE. WILLOW FAMILY. 



Salix, Tourn. 



S. tristis, Ait. Dwarf Gray Willow. 



Not uncommon. Apr.-May. 

 S. humilis, Marsh. Prairie Willow. 



Rather common. " The intermediate character of this species, as 



between S. tristis and S. discolor was long ago pointed out by Mr. 



Carey. The confusing forms appear to be hybrids." — M. S. Bebb. 

 S. discolor, Muhl. Glaucous Willow. 



Common. Forms with anthers transformed to ovaries, occasional. 



Apr.-May. 



