52 



5. Populus tremuloides Michaux. QUAKING ASPEN. Plate 19. 

 A straight narrow tree up to 3 dm. in diameter, usually about 1-5 dm. 

 in diameter; bark usually smooth, greenish-white or gray, on older 

 trees becoming rough or fissured, and turning darker; shoots glabrous 

 or with a few hairs, turning reddish-brown the first season, later to 

 a gray; leaves of sprouts and very small trees usually ovate with a 

 cordate base and two or three times as large as leaves of older trees; 

 mature leaves on older trees variable, glabrous, the prevailing type has 

 a bluish-green leaf which is widely ovate or nearly orbicular, 3-7 

 cm. long, truncate or slightly rounded at the base, usually abruptly 

 short-pointed at apex, finely and regularly serrate, the unusual type 

 of leaf is thinner, yellow-green, ovate, % as wide as long, rounded 

 or wedge-shaped at base, gradually tapering to a point at the apex, 

 otherwise as the prevailing form; stamens 6-12; capsules about 6 mm. 

 long, on stalks about 1 mm. long; wood light, soft and weak. 



Distribution. One of the most widely distributed of North 

 American trees. It ranges from Labrador south to Pennsylvania, thence 

 southwest to northern Mexico, and then north to northern Alaska. It is 

 found at sea level and at elevations of 10,000 feet. There are records 

 of its occurrence in all parts of Indiana. In all of its Indiana stations 

 it grows only in low ground about lakes, swamps, ponds, low places 

 between sand dunes, and along streams. In many places in the lake 

 region it is found in almost pure stands over small areas. 



Remarks. In Indiana this species is not of sufficent size and 

 abundance to be of much economic importance. 



JUGLANDACEAE. THE WALNUT FAMILY. 



Trees with large, aromatic, odd pinnate leaves; flowers appearing 

 after the leaves unfold, the staminate in catkins, the pistillate solitary 

 or in clusters ; fruit a nut in a fleshy or hard fibrous shell ; kernel edible 

 or astringent. 



Pith of twigs chambered; staminate catkins thick, sessile or 

 short stalked; stamens 8-40, glabrous; nuts with a network 

 of rough projections 1 Juglans. 



Pith of twigs not chambered; staminate catkins slender, long- 

 stalked; stamens 3-10, hairy; nuts more or less angled but 

 smooth 2 Carya. 



1. JUGLANS. THE WALNUTS. 



Trees with furrowed bark; pulp surrounding nut continuous, without 

 lines of dehiscence on the surface. 



