Subclass 2. DICOTYLEDONES. 



Embryo mostly with 2 seed-leaves, if with only one seed-leaf, 

 the first leaves opposite. Stem exogenous, i. e., differentiated into 

 pith, wood, and bark; fibro-vascular bundles arranged in concen- 

 tric layers around the pith, the new bundles being formed between 

 the wood and the bark. Leaves usually pinnately or palmately 

 veined, with ramifying veins. Parts of the flowers mostly in 5's, 

 less commonly in 4's or 2's, seldom in 3's. 



Family 30. SALICACEAE. Willow Family. 



Dioecious trees or shrubs, with soft wood and simple alternate leaves. 

 Flowers in bracted aments, solitary in the axils of scale-like bractlets. Peri- 

 anth represented by one or more glands or a cup-like disk. Stamens one 

 or more. Pistil solitary, with 2-4 parietal placentae, becoming a dehiscent 

 capsule; seeds numerous, bearing a tuft of hairs at the apex; endosperm 

 wanting. 



Bractlets incised; flowers with a cup-shaped disk; stamens usually more than 10; stigmas 

 expanded ; winter-buds with several scales 1. PoPULUS. 



Bractlets entire or denticulate; flowers with one or more glands; stamens 2-7. in most 

 species only 2; stigmas narrow; winter-buds with but 1 scale each. 2. Salix. 



Q 1. P0PULUS (Tourn.) L. Poplar, Cottonwood, Aspen. 



Trees, with furrowed bark and often resinous buds of more than one scale. 

 Leaves petioled, usually with broad, toothed or even lobed blades, and caducous 

 stipules. Flowers in drooping aments; bractlets membranous, lobed or fimbriate 

 at the apex, usually caducous. Disk present, oblique, entire, toothed, or lobed. 

 Stamens adnate to the disk; filaments distinct, glabrous; anthers purple, orange, 

 or red. Ovary sessile in the disk; style short; stigmas 2-4, dilated. Ovules 

 anatropous. Capsule opening by 2-4 valves. 



Leaves not white-tomentose beneath, toothed or rarely entire. 

 Petioles strongly flattened laterally. 



Leaves suborbicular, acute or very short-acuminate, finely crenate or subentire. 

 Leaf-blades witii 2 conspicuous glands beneath at the base. 



1. P. cercidiphylla. 

 Leaf-blades not glandular at the base. 2. P. tremuloides. 



Leaves broadly deltoid, cordate, or ovate, abruptly acuminate, coarsely toothed, 

 especially about the middle. 

 Cup of the pistillate flowers 6-8 mm. broad. 



Pedicels equalling or exceeding the capsules ; leaf-blades longer than broad ; 



teeth few, less than 10 on each side. 3. P. Wislizeni. 



Pedicels shorter than the capsules ; leaf-blades usually broader than long ; 

 teeth more than 10 on each side, sometimes obscure. 



4. P. Fremontii. 

 Cup of the pistillate flowers less than 5 mm. broad; teeth of the leaves many, 

 more than 10 on each side; pedicels shorter than the capsule. 

 Leaves flabellate-cordate, with a broad, concave, entire sinus. 



.5. P. Sargeniii. 

 Leaf-blades ovate, roimded or cuneate at the base, which is more or less 

 toothed ; only the blades of the young shoots cordate. 



6. P. Besseyana. 

 Petioles terete or nearly so. 



Petioles at least half as long as the blades ; blades cordate, ovate, or broadly lan- 

 ceoiate. 

 Leaves green on both sides, abruptly long-acuminate. 7. P. acuminata. 



Leaves paler beneath, acute or somewhat acuminate. 

 Fruit sessile, usually 3-carpellary. 



Ovary and capsule densely pubescent, subglobose. 8. P. trichocarpa. 



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