_Trees_ and _shrubs_ with small, unisexual, _monœcious_ flowers, having no perianth or a simple inconspicuous one. The ♂ and ♀ flowers are very different and generally placed in separate inflorescences. The ♂-flowers are most often adnate to the bracts. The stamens are placed _opposite the perianth-leaves_, when they are present in equal numbers. The ♀-flower is _naked_, or has a _superior_ perianth. The ovary at the base is 2- or 3-(-6) locular with 1 or 2 pendulous ovules in each loculus, only one of which is developed; the fruit is a one-seeded _nut_; _endosperm absent_; embryo straight. The inflorescences, which are either compound and mixed (small dichasia in spikes) or simple, are here also termed _catkins_; but, strictly speaking, this term is applied to the ♂-inflorescences only. In all Quercifloræ the leaves are _scattered_ (usually in 2 rows) _simple_, and _penninerved_, and with _deciduous stipules_. It is worthy of remark that in _Betulaceæ_, _Corylaceæ_ and _Quercus_ the ovules, and to some extent the loculi of the ovary are not developed till after pollination, so that the development of the pollen-tube proceeds very slowly. The smallness of the flowers, the absence of honey, the dryness and lightness of the pollen, the size of the stigma and the abundance of hairs found on many stigmas are all adaptations for wind-pollination. It is also an advantage that the flowers are generally pollinated before the foliage-leaves are developed, thus preventing the pollen being entangled by the leaves. The two orders _Betulaceæ_ and _Corylaceæ_ mentioned here are by other authors united into one order. [It is doubtful whether these two should be retained in the family Quercifloræ, as recent researches (p. 273) have shown that they differ from the Cupuliferæ in many important points, and agree with the Casuarinas in the fact that the pollen-tube enters the ovule through the chalaza.] Order 1. =Betulaceæ= (=Birches=). Monœcious, with thick, cylindrical, _compound_ ♂ and ♀ inflorescences (2- or 3-flowered dichasia in a spike with spirally-placed floral-leaves) (Figs. 324, 326, 328). When the perianth in the ♂-flower is completely developed, it is composed of 4 somewhat united leaves, which are placed opposite the 4 stamens (Figs. 325, 326 _A_). The female flowers are _naked_; the ovary is bilocular, with two styles and one _pendulous_ ovule in each loculus. The subtending floral-leaves unite with the bracteoles and form a 3–5-lobed cover-scale, which is not attached to the fruit (Figs. 325 _D_, 326 _B_). Fruit a _nut without cupule_ (see _Corylaceæ_ and _Cupuliferæ_). ~In the bud the leaves are flat. The stipules are deciduous. On germination the cotyledons are raised above the ground. Terminal buds are only found on old Alder trees; the Birch has sympodial branches.~