18 ELEMEKTS OF BOTANY. 



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. 



c. (P. monilifera), Cottoxwood. a large and very rapidly 

 growing tree, 75 to 100 or more ft. in height, often with a markedly 

 excurrent trunk (Fig. 26). Leaves large and broadly triangular, 

 with crenate-serrate margins and long tapering acute tips ; petioles 

 long and considerably flattened. The numerous pediceled capsules 

 are quite conspicuous when mature, and the air is filled with the 

 downy seeds at the time when the capsules open. 



CUPULIFERS, OAK FAIMILY. 



MoncBcious trees or shrubs. Leaves alternate, simple, 

 straight-veined, with deciduous stipules. The staminate 

 flowers are generally in catkins, the pistillate ones some- 

 times in catkins, sometimes not. The ovary is several-celled, 

 with one or two ovules in each cell, but only one ovule 

 matures to form the fruit, which is a 1-ceIled and 1-seeded 

 nut (Fig. 170). 



I. BETULA, BIRCH. 



Flowers opening in early spring, the staminate ones in 

 long and drooping bright yellow catkins, which appear with 

 or before the leaves, the pistillate ones in much shorter and 

 stouter catkins. Each scale of the staminate catkins bears 3 

 flowers, which consist mainly of two 2-parted filaments, with 

 an anther-cell on each. On every scale of the pistillate cat- 

 kins are borne 2 or 3 flowers, each of which consists simply 

 of a naked ovary with two diverging stigmas. 



a. (B. LENTA), Sweet, Black, or Cherry Birch. Leaves 

 and bark with the agreeable smell and flavor of wintergreen. 

 Leaves more or less heart-shaped at the base, ovate or nearly so, 

 doubly serrate. A tree 50 to 75 ft. high, with beautiful pale rose- 

 colored wood, used in cabinet work under the name of red birch. 



h. (B. popuLiFOLiA), Gray Birch. Leaves triangular, with a 

 long taper point and truncate base, unevenly twice serrate, with 

 longish slender petioles, which allow the leaves to quiver like those 

 of the aspen. Bark scaling off in white strips and layers, but not in 

 nearly as large sheets as that of the rarer canoe birch (B. -papyriferd). 



