BETDLACEAE (BIRCH FAUlLy) 336 



Vs. B. nigra L. (River or Red B.) Tree with greenish-brown somewhat 

 laminate barli and reddish twigs ; leaves acutish at both ends, when young 

 downy underneath ; petioles, peduncles, and thick-cylindrio catkins tonientose ; 

 bracts with oblong-linear nearly equal lobes. — Banks of streams and in swamps 

 e. of the Allegheiiies from e. Mass. to Fla., thence w. to Tex.; and through the 

 bottom-lands of the Mississippi R. system. 



*• * Trees or shrubs with slender cylindric fruiting catkins, their scales readily 

 deciduous ; leaves (^of the fruiting branches) with 7 or less pairs of 

 prominent veins. 



■ir- Wing distinctly broader than the body of the fruit ; trees or stout shrubs with 

 white, whitish, or brown papery bark. 



•w- Bark dull, chalky- or ashy-white, smooth and close, the layers not readily 

 exfoliating ; staminale catkin usually solitary. 



4. B. populif61ia Marsh. (White, Gray or Old Field B.) Trunk usually 

 ascending, rarely 10 m. high; leaves triangular (deltoid), very taper-pointed 

 (usually abruptly), truncate or nearly so at the broad base, smooth and shining 

 both sides, except for the resinous glands when young, tremulous on very slender 

 petioles ; fruiting catkins slender-stalked, ascending, 1-3 cm. long, 5-7 mm. thick ; 

 the drab or ashy-brown wide-spreading scales 2.6-4 mm, long, their lubes puberu- 

 lent. — Poor sandy or rooky soil, commonest near the coast, P. E. I. to Del., w. 

 to L. Ont. 



M. ++ Bark lustrous, creamy- or pinkish-white to bronze, freely splitting into 

 paper-like layers ; staminate catkins mostly 2 or 3. 



= Branchlets and leaves strictly glabrous from the first. 



5. B. p€ndula Roth. (White or Canoe B.) Branches slender and flexuous, 

 often drooping, the branchlets usually verrucose with resiniferous atoms ; leaves 

 glutinous when young, firm, rhombic-ovate to deltoid or broad-ovate, subcuneate, 

 truncate, or subcordate at base, long-acuminate, slender-petioled ; fertile catkins 

 pendulous, 1.5-3 cm. long, 6-9 mm. thick ; the ascending brown or straw-colored 

 scales 3-5 mm. long, glabrous except for the ciliate margin. (B. verrucosa 

 Ehrh.) — Rocky upland woods and slopes, Que. to Alaska, locally s. to Me., A''t., 

 111., Man., etc. (Eurasia.) —A polymorphous boreal species, of which the N. E. 

 phase has recently been designated as B. caerulea Blanchaid (Blue B.). 



= = Branchlets puberulent or pubescent ; young leaves (except in var. minor) 



pubescent beneath. 



6. B. SlbaL. (Paper, Canoe or White B.) Branches and branchlets ascend- 

 ing ; resiniferous atoms, if present, mixed with long hairs ; leaves ovate, taper- 

 pointed, from rounded to cuneate at base, in maturity 3-6 cm. long, smooth and 

 green above, pale, glandular-dotted, and a little hairy on the veins beneath, sharply 

 and unequally double-serrate; fruiting catkins 1.5-4.5 cm. long, 0,5-1.5 cm. 

 thick, spreading or drooping on slender peduncles ; the mostly ciliate-margined 

 ascending scales 3-7 mm. long. (B. pubescens Ehrh.) — Large shrub or medium- 

 sized tree, Nfd. to B. G., s. to N. E., the Great Lake region, etc. (Eurasia.) 

 Passing to the commoner American 



"Var. papyrifera (Marsh.) Spach. Usually a larger tree, with mature leaves 

 6-9 cm. long. (B. papyrifera Marsh.) — Nfd. to Alaska, s. to Pa., Ind., n. la., 

 Neb., Wyo., and Wash. 



Var. glutinftsa (Wallr.) Trautvetter. Branches pendulous ; leaves 3-5 cm. 

 long, pilose on the veins beneath ; catkins on straight peduncles. — Wassataquoik 

 Valley, Me., (Ku.) 



Var. cordif&Iia (Regel) Fernald. Leaves broad-ovate, cordate, pilose on the 

 veins beneath. — Cool woods and mts.. Lab. and Nfd. to B. C, s. to N. E., L. 

 Superior, la., and westw. — Becoming a dwarf shrub on alpine slopes. 



Var. minor (Tuckerm.) Fernald. Stout dwarf shrub ; leaves elliptic- or 

 truncate-ovate, glutinous, glabrous, 1.5-4 cm. long; staminate catkin often soli- 

 tary ; fruiting catkins mostly ascending, 1.3-3 cm. long, 0.5-1 cm. thick. iB. 



