236 SYSTEMATIC BOTANY 



The Poplars (Populus) also belong to this order (see Fig. 

 186). 



Order Betulaceae. 1 Shrubs or trees with simple 

 stipulate leaves. Flowers in terminal catkins. Monoe- 

 cious, and usually arranged in small three-flowered 

 cymes in the axils of the bracts of the catkin (Fig. 188). 

 Perianth reduced. Ovary inferior ; carpels two, syn- 

 carpous, two-celled, one ovule in each cell. Fruit a one- 

 seeded indehiscent nut. 

 This order includes several well-known trees, e. g. Birch 

 (Betula alba), Alder (Alnus glutinosa), Hazel (Corylus 

 Avellana), and Hornbeam (Carpinus Betulus) (see Figs. 187, 

 188, 189, pp. 282-7). 



Order Fagaceae. 1 Trees with simple stipulate leaves. 



Flowers in axillary catkins, monoecious. Perianth 



lobes 5-6. Carpels three, syncarpous. Ovary inferior, 



usually three-celled with two ovules in each. Fruit 



a one-seeded nut. Nuts enclosed in a cupule (see 



Fig. 191, p. 290). 



The order includes many forest trees, e. g. Oaks (Quercus 



spp. 2 ), Beech (Fagus sylvatica), and Sweet Chestnut (Cas- 



tanea sativa). 



Order Ranunculaceae. The perianth is indefinite, often 

 petaloid and polypetalous. Stamens indefinite and 

 hypogynous. Pistil superior. Carpels indefinite and 

 usually apocarpous. Fruit a group of achenes or 

 follicles (Figs. 144 and 149). The flowers may be 

 cyclic: Aquilegia; hemicyclic : Ranunculus; acyclic 

 or spiral : Aconitum, Helleborus. 



The plants of this order are chiefly North Temperate, 



1 The orders Betulaceae and Fagaceae are very closely related, 

 and sometimes placed in one order, Cupuliferae. 



2 Spp. after a generic name means there are several species in 

 the genus. 



