TREES, SHRUBS, AND FORESTS 



385 



Reproduction. The white oak is monoecious, with the imperfect 

 flowers borne on the young shoots and the twigs of the previous 

 season (Fig. 238). The male flowers occur in loose spikes or 

 catkins, and the female flowers in few-flowered spikes in the axils 

 of leaves above the clusters of male catkins. Each male flower 

 is composed of a group of from 5 to 8 stamens in an inconspicuous 

 perianth with from 5 to 9 

 lobes. Each female flower is 

 composed of a single pistil 

 with a rudimentary perianth. 

 The two or three pistillate 

 flowers which occur in a single 

 spike are enveloped in a cup 

 formed of coherent bracts, 

 which ultimately develop into 

 the cupule, or cup, of the fruit. 



Pollination is by the wind 

 (anemophilous). For this the 

 white oak is adapted by its 

 abundant light pollen grains 

 produced in pendent catkins, 

 which are easily swayed by 

 air currents. 



The fruit is a nut, or acorn, 

 resting in the cupule, or cup, 

 formed, as indicated above, 

 by bracts which surround each 

 spike of female flowers. In 

 the white oak the acorn matures each fall, unlike the black-oak 

 series, in which the acorn ripens the second season after pollina- 

 tion. The acorn germinates in the fall, sending a long taproot 

 deep down into the soil. The plumule and root are liberated 

 from the seed by the lengthening of the petioles. The age at 

 which the white oak forms its seeds varies with the conditions 

 under which it is growing. Where trees grow in the open in 

 rich, well-watered soil, seed production may occur in the eighteenth 

 or twentieth year; in open woods it occurs at the age of forty 



Wvule. 



Female flower 

 in long section Acorn 



FIG. 238. Drawing of the inflorescence, 

 flowers, and fruit of the white oak 



