THE DICOTYLEDONES 



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composed of two carpels. There is a single ovule in each loculus which 

 is anatropous and pendulous, possessing a single integument and an out- 

 wardly directed micropyle. The seed is endospermic and the embryo 

 small. 



The plants are mostly herbaceous, though a few are woody and the 

 leaves are often compound and much divided. The flowers are usually 

 small and are arranged in umbels. Oil or resin canals are often present. 



This order is characterized by a simplification of the structure of the 

 flower and is sharply defined. It contains only three families, Araliaceae, 

 Umbelliferae and Cornaceae. We shall consider the Umbelliferae in detail 

 but will first indicate certain points of interest in the other two families. 



The Araliaceae are a small family, containing about fifty-five genera 

 and some 700 species, which are chiefly tropical, with their centres of 

 distribution in Indo-Malaya and tropical America. The plants are usually 

 trees or shrubs; many are climbers. The leaves are usually alternate, often 

 large and compound, with small stipules. The flowers are small but are 

 developed in large compound umbels. Each flower has four very small 

 sepals, five petals and stamens and the gynoecium consists of five carpels 

 forming a quinquelocular ovary, each loculus having a single, pendulous 

 ovule. The fruit is a drupe. 



The most important genus is Hedera, with six temperate species; 

 H. helix (Ivy) is a root climber with dimorphic leaves, those on the 

 vegetative shoots being palmate and those on the flowering shoots being 

 simple. The flowers (Fig. 1748) are not conspicuous but develop late in 

 the year and are pollinated by flies and hive bees. It is a native of Europe 



Fig. 1748. — Hederahelix. Uy. Flowering shoot with unlobed leaves. 



