Roscndahl: observations on betula 455 



nent bark of older twigs and branches ; leaves with 4-5 pairs of 

 veins, rhombic-ovate to obovate, cuneate or sometimes rounded at 

 the base, broadly acuminate or rounded at the apex, 2.5-5.5 cm. 

 long, 1.5-3.5 cm. wide, (on sterile shoots usually more broadly 

 ovate and larger, 5-7 cm. long, 4-5 cm. wide, dentate and more 

 pubescent throughout), serrate, the serrations somewhat crenate 

 and occasionally uneven, pubescent beneath, especially along the 

 veins, at length becoming nearly or cjuite glabrous, dotted with fine 

 resinous glands, dull green above, lighter beneath, thick and firm 

 in texture, finely reticulate-veined, the reticulations conspicuous on 

 the upper surface in dried specimens; petioles 7-13 mm. long; 

 staminate catkins borne singly or in pairs at the ends of the 

 branches, 3-5 cm. long, 5 mm. thick; pistillate catkins 10-14 mm. 

 long, 1.5-2 mm. thick, pedicelled, bearing 1-2 leaf-like bracts; fruit- 

 ing catkins cylindrical, erect, 2-2.5 cm. long, 6-7 mm. in diameter, 

 pedicel about 1 cm. long, bracts 4 mm. long, about 3.6 mm. wide, 

 lateral lobes spreading, shorter than the tapering middle lobe, 

 puberulent on the back and finely ciliate-pubescent along the mar- 

 gins of the lobes; samara 3.2-3.5 mm. wide, nutlet 1.3 mm. wide, 

 mostly slightly narrower than the wing. (Fig. 1, c-e, fig. 2, g-h.) 



Infrequent in tamarack swamps. Has been found in four differ- 

 ent swamps of Hennepin County, in each case associated with the 

 parent species. Also reported from Saskatchewan and Montana. 

 To what extent if any the hybrid breeds true, it is impossible to 

 say, but most of the plants so far found are quite uniform in size, 

 mode of branching and growth, color of bark, texture of leaves, 

 fruiting catkins, etc. They may all, however, be hybrids of the F^ 

 generation since they occur where the parent species abound. One 

 notable exception has been observed which may conveniently be 

 designated and described as : 



Forma maxima. Very large spreading shrub or small tree,' with 

 3-4 irregularly branching stems from a common root, 8-10 m. 

 high, 12-17 cm. in diameter; bark gray, peeling slightly into 'thin 

 layers, young twigs glabrous, branches slender and somewhat pen- 

 dulous ; leaves rhombic-ovate to obovate, distinctly cuneate at the 

 base, acute or rounded at the apex, 3.5-6.5 cm. long, 1.5-4.5 cm. 

 wide, mostly coarsely serrate to dentate, glabrous or with only 

 a few scattered hairs along the veins, finely reticulate- veined ; 

 petioles 12-17 mm. long; fruiting catkins 2.5-3.6 cm. long, 7-9 mm. 



