DICOTYLEDONES 



419 



cus), Chestnut (Castanea), and Beech (Fagus). These are among the most im- 

 portant forest trees of cold temperate regions, where the Oaks and Beeches 

 sometimes constitute the whole of the forest growth. 



The flowers (Fig. 400) are, with very rare exceptions, monoacious, the stami- 

 nate in drooping catkins, the pistillate solitary. The fruit is a nut, which not 

 infrequently is enclosed by an involucre or thickened envelope, formed from the 

 bracts surrounding the flower. This involucre forms the "cup" in the acorn, 

 and in the Beech and Chestnut is the spiny husk in which the nuts are enclosed. 



A 



FIG. 401. A-C, Ulmus campestris, var. suberosa. A, flower with stamens and 

 pistil. B, pistil showing the two stigmas. C, young samara, or winged fruit. 

 D-G, Morus alba. D, male catkins. E, single male flower, enlarged. F, female 

 inflorescence (X 2). G, Ripe fruits. 



Order IX. Urticales 



The Urticales comprise a large number of herbs, shrubs, and trees, being espe- 

 cially well represented in the warmer parts of the world. The flowers are usually 

 diclinous, but may be hermaphrodite. They are generally born* in dense inflo- 

 rescences of various kinds (Fig. 401). A single perianth is usually present, 

 but is inconspicuous, and may be entirely absent. The stamens are generally 

 attached to the perianth, which is often persistent, and may become pulpy and 

 form a pseudocarp. The fruits (syncarps) of the Mulberry (Fig. 401) and Osage 

 Orange (Maclura) are of this nature. 



There are three families, Ulmacese, to which belong the Elms (Ulmus) and 

 Hackberry (Celtis) ; the Nettle family (Urticaceae), largely composed of herba- 

 ceous plants ; and the Mulberry family, MoraceaB, which is composed of trees, 



