ORDER 126. CYCADACEJE. 311 



21 S. petloltiris Sm. Shrub 4 15f, twigs long, slender, tongh, 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. 

 13. xrrtcta. Lvs. grayish-silky beneath ; stigma sessile ; stipules deciduous. 



2. POPULUS, Tourn. POPLAU. ASPEN. Aments cylindric, scales 

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

 8 30. 2 Ova. free, stig. very large, 2-lobed. Caps. 2-valved, 2-cdled. J> 

 Large trees, with soft, light wood. Leaves broad, 6n long, often com- 

 pressed petioles. Aments lateral, before the leaves. 



Bud? not viscid. Leaves lobed, al-vays white-downy beneath No. 1 



Buds not viscid. Leaves round-ovate, soon glabrous and green Nos. 2 4 



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



x Leaves ovate whitened beneath. Stamens 2030 Nos. 5, 6 



x Leavi-s deltoid or deltoid-ovat Stain. 6 30. Petioles compressed.. Nos. 7 9 



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



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



2 P. treanuloides 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. heteropliylla 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. tii-amlidoiiUtta MX. Tree some 40f. with smoothish gray bark; Ivs. round- 



ovate, acute, with large unequal sinuate teeth, villouw when young ; buds subpubes- 

 cent ; petioles compressed. Woods. Common northward. 



5 P. balsamifera L. Balsam P. Tacmetiac. Tree 40 80f, with rough bark; Ivs. 



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



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



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



7 P. aiigulata, Ait. Western Cotton-wood. Tree -iO 80f, branches acutely angular 



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



8 P. Canad^nsls De-f. Necklace Cotton-wood. Tree 40 80f; young branchlets an- 



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

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



9 P. nlgra, /3. betuli folia. Black P. Tree wiih an ovoid form, 30 40f ; young 



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

 y. (tilat'ata. Lombardy P. Tree very tall, pyramidal in form ; Ivs. deltoid. Com. 



CLASS II. GYMNOSPERM^E. 



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 CXXVI. CYCADACE^E. CYCADS. 



Tree* of low stature, simple trunks with their mternodes undeveloped 

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



