ORDER ISO. CYCADACE^E. 311 



21 S. petiolaris Sm. Shrub 4 15f, twigs long, slender, tough, purplish or yellow- 

 ish ; Ivs. linear-lanceolate, smooth, glaucous beneath ; stipules lunate, dentate ; ova- 

 ries ovoid, densely silky, stigmas very short. Sandy banks of streams. 

 /3. ftericea. Lvs. grayish-silky beneath ; stigma sessile ; stipules deciduous. ' 



2. FOPULUS, Tourn. POPLAR. ASPEN. Aments cylinclric, scales 

 lacerate-fringed. Cal. an oblique, disk-like cup, its margin entire. $ Sta. 

 830. $ Ova. free, stig. very large, 2-lobed. Caps. 2-valved, 2-celled. *> 

 Large trees, with soft, light wood. Leaves broad, on long, often com- 

 pressed petioles. Anients lateral, before the leaves. 



Buds not viscid. Leaves lobed, always white-downy beneath No. 1 



Buds not viscid. Leaves round-ovate, soon glabrous and green Nos. 24 



Buds viscid with a resinous varnish. Leaves always glabrous. . . (x) 



x Leaves ovate, whitened beneath. Stamens 2030 Nos. 5. 



x Leaves deltoid or deltoid-ovata Stain. 6 30. Petioles compressed.. Nos. 7 9 



1 P. ALBA. AbeleP. Silver-leaf P. Tree rapidly growing, and spreading by the roots ; 



leaves cordate, lobed, dark green above, very white beneath. Europe. 



2 P. tremuloides MX. American Aspen. Tree 25 40f; bark smooth, greenish; 



Ivs. roundish-cordate, abruptly pointed, dent-serrate ; petioles compressed, rendering 

 the leaves tremulous in the slightest breeze. Woods : common. 



3 p. Iieteropliylla L. Cotton-wood. Tree 40 60f, with smooth greenish bark ; Ivs. 



roundish, cordate or ovate, serrate, white-downy when young ; buds very downy, 

 short, obtuse ; stamens very many ; seed with much cotton. Wet woods. 



4 P. graiidldeiitata MX. Tree some 40f, with smoothish gray bark ; Ivs. round- 



ovate, acute, with large unequal sinuate teeth, villous when young ; buds eubpubes- 

 cent ; petioles compressed. Woods. Common northward. 



5 P. balsa in if era L. Balsam P. Tacmehac. Tree 40 80f, with rough bark; Ivs. 



ovate, acuminate, with appressed serratures ; buds very fragrant. Wei. N. 



6 P. caiidicans Ait. Ralm-of-Gilead. Tree 30 50f; Ivs. ovate, cordate, acuminate, 



serrate ; petiole hairy ; buds full of fragrant resin. Woods, and cultivated. 



7 P. angulata. Ait. Western Cotton-wood. Tree 40 80f, branches acutely angular 



or winged ; leaves deltoid-ovate, or broad-cordate : buds little viscid. S. and W. 



8 P. Caiiadensis Desf. Necklace Cotton-wood. Tree 40 80f; young branchlets an- 



gular ; Ivs. deltoid to oval, acuminate, erose-denticulate, subcordate ; ament Bcales 

 not hairy. By rivers and lakes, N. and W. (P. monilifera Ait.) 



9 P. nfgra, /3. betuliroUa. Black P. Tree with an ovoid form, 30 40f ; young 



branches and Ivs. pubes. ; Ivs. deltoid-rhombic, pointed, crenate-serrate. N. Y. : rare, t 

 y. dilatata. Lombardy P. Tree very tall, pyramidal in form ; Ivs. deltoid. Com. 



CLASS II. GYMNOSPERM2E. 



Pistils none, or represented by open scales, with ovules in 

 their axils. Stigma none, but the pollen applied directly to the 

 ovules, which become naked seeds, destitute of a true pericarp. 

 Flowers always diclinous. Cotyledons often more than 2. (510.) 



COHORT 4. CONOIDE^E. Equivalent to the Class. ( 515.) 



ORDER CXXVL CYCADACEJ3. CYCADS. 



Trees of low stature, simple trunks with their mternodes undeveloped 

 and the surface scarred with the fallen leaves. Leaves pinnate, parallel- 



