DICOTYLEDONOUS PLANTS 47 



SUBCLASS II.— DICOTYLEDONOUS PLANTS. 



Stems composed of bark, wood, and pith ; the fibro-vascular 

 bundles in rings ; in woody stems which live over from year 

 to year, the wood generally in annual rings, traversed. at right 

 angles by medullary rays. Leaves netted-veined. Parts of 

 the flower usually in fours oj' fives. Cotyledons 2 (rarely 

 none). 



14. SALICACE.^;. Willow Family. 



Dioecious trees or shrubs, with flowers in catkins (Ch. XIII), 

 destitute of floral envelopes. Fruit a 1-celled pod, with 

 numerous seeds, provided with rather long and silky down, 

 by means of which they are transported by the wind. 



I. POPULUS, Toum. 



Trees with prominent scaly buds, twigs more or less angled. 

 Leaves usually long-petioled. 



Flowers borne in long, drooping catkins, which appear 

 before the leaves ; scales of the catkins irregularly cut toward 

 the tip. Stamens 8-30 or mpre. Stigmas 2-4. Capsules 

 opening early by 2 to 4 valves. 



1. P. tremiiloides, Michx. American Aspen, Quaking Asp. A 

 tree 20 to 60 ft. high, with greenish-white bark ; leaves roundish, 

 heart-shaped, abruptly pointed, with small regular teeth. Leaf- 

 stalk long, slender, and flattened at right angles to the broad 

 surfaces of the leaf, causing it to sway edgewise with the least per- 

 ceptible breeze. Common especially N. 



2. P. grandidentata, Michx. Large-toothed Poplar. A tree 

 60 to 80 ft. high, with rather smooth gray bark ; leaves 3-5 in. long, 

 roundish ovate and irregularly sinuate-toothed; when young com- 

 pletely covered with white silky wool, which is shed as soon as the 

 leaf matures. The petiole is somewhat flattened, but not nearly as 

 much so as that of the preceding species. Rich woods N. 



3. P. heterophylla, L. Swamp Poplar. Branches only slightly 

 angled. Leaves ovate, mostly obtuse at the apex, rounded or sub- 

 cordate at the base, serrate with obtuse teeth, densely woolly when 



