94 MIDDLESEX FLORA. 



COMPTONIA, Soland. 

 C. asplenifolia, Ait. SWEET FERN. 

 Common. Apr.-May. 



BETULACE^E. BIRCH FAMILY. 



BETULA, Tourn. 



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. v? r. populifolia, Spach. AMERICAN WHITE BIRCH. 

 GRAY BIRCH. 

 Common. May. 



B. papyracea, Ait. WHITE BIRCH. PAPER or CANOE BIRCH. 

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

 June. 



B. papyracea, Ait., var. minor, Tuckerm. 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 Valley. 



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. 



SALICACE>E. 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. 



