CLASSIFICATION OF DICOTYLEDONS. 183 



numbers in drooping catkins at the ends of the branches, 

 shedding the pollen in early spring before the leaves unfold. 

 The female flowers are produced on the same branches, but 

 lower down, and in much smaller numbers. The stigmas are 

 long, and covered with minute hairs that catch the pollen which 

 is shaken out in clouds every time the plant is shaken by the 

 wind, and falls in a shower over the stigmas. A similar 

 arrangement is seen in the oaks, hickories, and walnuts. 



There are three orders of the luliflorce : Amentacece, Piperi- 

 nece, and Urticinee. The first contains the birches (Betulacece) ; 

 oaks, beeches, hazels, etc. (CupuUferce) ; walnuts and hickories 

 (Juglandem) ; willows and poplars (Salicacece). They are all 

 trees or shrubs ; the fruit is often a nut, and the embryo is 

 very large, completely filling it. 



The Piperinece are mostly tropical plants, and include the 

 pepper plant (Piper), as well as other plants with similar 

 properties. Of our native forms, the only common one is the 

 lizard-tail (Saururus), not uncommon in swampy ground. In 

 these plants, the calyx and corolla are entirely absent, but the 

 flowers have both carpels and stamens (Fig. 97, H). 



The Urticince include, among our common plants, the nettle 

 family (TJrticacece) ; plane family (Platanece) , represented by 

 the sycamore or buttonwood (Platanus) ; the hemp family 

 (Cannabinece) ; and the elm family (Ulmacece). The flowers 

 usually have a calyx, and may have only stamens or carpels, 

 or both. Sometimes the part of the stem bearing the flowers 

 may become enlarged and juicy, forming a fruit-like structure. 

 Well-known examples of this are the fig and mulberry. 



The second group of the Choripetalce is called Centrospermte, 

 and includes but a single order comprising seven families, all 

 of which, except one (Nyctaginece) , are represented by numer- 

 ous native species. The latter comprises mostly tropical plants, 

 and is represented in our gardens by the showy "four-o'clock 7 ' 

 (Mirabilis'). In this plant, as in most of the order, the corolla 

 is absent, but here the calyx is large and brightly colored, 



