The Alders 259 



die, the lateral lobes ascending, the stalk-Uke part below the lobes linear-wedge- 

 shaped; the nut is oblong, acute at both ends, 3 to 4 mm. long, rather wider than 

 its wings. 



The tree grows rapidly and is a striking element in the northern forests, its 

 silvery gray or yellowish bark being quite different from any other. The hard, 

 strong wood is extensively used for furniture, boxes, tools, hubs, and for fuel; it 

 has a specific gravity of about 0.65 and takes a good polish. 



V. THE ALDERS 



GENUS AUOJS [TOURNEFORT] HILL 



?|BOUT 25 species of Alders are known, distributed nearly throughout 

 the north temperate zone, extending in America south through Central 

 and South America, along the Andes, to Bolivia. The generic name 

 is of Celtic origin, in allusion to the growth of these shrubs and trees 

 along streams, and was adopted later from earlier authors. Other American 

 species than those here described are A. jorullensis H. B. K., A. acuminata 

 H. B. K., and A. arguta H. B. K., and other species in Mexico, A. acuminata H. 

 B. K. extending to Peru and Bolivia. A. jerruginea H. B. K. occurs in Colombia. 

 We have also several shrubs. The genus is not represented in the West Indies. 

 The wood of Alders is soft and weak, the sap watery and the bark astringent, 

 being used to some extent for tanning. The leaf-buds are naked, small, usually 

 red, the blades of the leaves being enclosed in their stipules in the bud; the stipules 

 fall away when the leaves unfold. The leaves are variously toothed or lobed, 

 pinnately veined, with the veins usually prominent on the imder side. The 

 flowers are very small, monoecious (dioecious bushes of A. serrulata Willdenow 

 have been observed), apetalous, densely clustered in catkins, the staminate catkins 

 long and drooping, the pistillate short and erect ; the flowers expand either in very 

 early spring before or with the leaves, or in a few species in late summer or autumn, 

 long after the leaves are fully grown. The staminate flowers are borne several 

 together (commonly 3) in the axil of each scale of the catkin; the calyx is usually 

 4-parted and there are from i to 4 stamens with short filaments. The pistillate 

 flowers are 2 or 3 together in the axil of each scale of the catkin; they have no 

 perianth, but are subtended by 2 to 4 minute bractlets; the ovary is sessile and 

 2-celled, each cell containing one suspended ovule; there are 2 slender styles, 

 which at the time of pollination project beyond the scales of the catkin. The 

 ripe pistillate catkins are oblong to ovoid; they remain on the plant for several 

 months, their scales becoming hard and woody, closely appressed to each other 

 at first, spreading when old and dry, lobed or crenate at the broadened apex. 

 The fruit is a minute nut with sharp margined or winged edges and contains a 

 single seed which has no endosperm. 



The European Betula Alnus Linnaeus is the type of the genus. 



