FOREST TREES OF THE PACIFIC SLOPE. 277 



mensely wide but storm-firm crowns. The hard, characteristically porous 

 wood (pores occupying mainly one portion of the annual layer) is exceedingly 

 strong in some oaks, and, with the hark, is astringent, due to the presence of 

 large amounts of tannin. 



The leaves of oaks occur singly on the branches — never in pairs, one opposite 

 another. The winter buds, rounded, angled, or pointed, are formed of overlap- 

 ping scales. Some oaks shed their leaves in autumn of each year: others, 

 have evergreen leaves, which are shed the second or third year. 



Male flowers, minute, arranged singly on thread-like stems, hang down in loose, 

 tassel like clusters from buds on twigs of the previous year's growth. Female 

 flowers, minute, very inconspicuous, bud-like bodies, are produced singly or 

 several in a stemmed cluster, from the bases of young growing leaves of the 

 spring; they develop into a nut-like fruit (acorn) in one or two seasons. 

 A notable exception to this arrangement of flowers is found in a section of the 

 genus Querats Pasania (treated by some authors as a distinct genus). In these 

 oaks, from 3 to 5 male flowers occur together, the groups are scattered along up- 

 right stems and grow singly from the bases of young leaves of the season (some- 

 times from the bases of the leaves of the previous year). Single female flowers 

 are also borne at some of these leaf-bases, usually at the uppermost ones. 



Flowers of all oaks are fertilized by the wind. The acorns which mature in 

 a single season grow steadily to full size during that period, while those which 

 mature in two seasons develop only very slightly the first summer (appearing 

 as miniature acorns), and begin to increase perceptibly in size only at the open- 

 ing of the second season. Mature acorns of annual-fruiting oaks are therefore 

 found on twigs of the year, while those of biennial-fruiting oaks are attached to 

 2-year-old twigs. By inspecting the biennial oaks in autumn or winter it 

 may always be determined whether or not they are to bear seed the following 

 season. Seed production is more or less periodic, at intervals ranging from 

 one to three years; but occasional trees bear fruit for several consecutive 

 seasons. 



The fruits, called acorns, are distinctive in having a separable, scaly — some- 

 times bristly — cup partly or almost wholly inclosing the smooth, thin-shelled nut. 

 Seed of the white-oak acorns is usually whitish, sweetish, and palatable, while 

 that of black-oak acorns is yellowish and bitter with tannin. In autumn, 

 when tlie nuts are mature, either the nuts fall from the cups or, in the less 

 easily separable fruits, both nuts and cups fall together. 



Under favorable conditions acorns may germinate in autumn, hut they com- 

 monly do not germinate until spring. The seed, or firm, inner body of the 

 acorn, consists of two seed-leaves, separated down the center, and from between 

 these, as germination proceeds, grow both the root, or radicle, and the main 

 stem of the little oak. Unlike those of some other trees, the seed-leaves of the 

 oaks do not form the first green, leaf-like organs, but remain in the split shell 

 and furnish nutriment to the growing stem and root until their supply is 

 exhausted, when they become black and later fall from the stem. A character- 

 istic of the seedling is the production of a very large, long taproot. This grows 

 for the first one or two years at the expense of the stem, which gains hut little 

 in height meantime. It enables seedlings repeatedly to survive ground fires 

 which kill the short stem. A new shoot may lie formed many times and the 

 little tree finally establish itself. 



Acorns are disseminated entirely through the agency of flood waters and 

 animals. .Mammals and birds eat them in large numbers and so reduce the 

 chances of reproduction, but by burying or otherwise storing them for winter 

 use they virtually plant them. 



