78(5 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



and project into the middle of the ovary. The androecium is composed of 5 or 

 many stamens which spring from the hypanthium, and are joined at the base to the 

 corolla. The fruit is baccate or capsular. The seeds contain no endosperm. 



The Cucurbitacese have symmetrical foliage-leavesno stipules, but often 

 tendrils (see vol. i. p. 696, fig. 165); the Begoniacese have oblique, unsymmetrical 

 laminae, large lacerated stipules, and no tendrils (see vol. i. p. 420, fig. HO 1 ). The 

 whorls of floral-leaves are 5-merous in Cucurbitacese; in Begoniacese the floral- 

 leaves of the female flowers are arranged in two whorls of 3-5 segments each, and 

 those of the male flowers in two whorls of 2-5 segments each. Three winged 

 ridges project from the inferior ovary in Begoniacese. The stalks of the ovules of 

 Cucurbitacese fill the cavity of the ovary so completely that only small interstices 

 are left between them. In many Cucurbitacese these stalks are converted when 

 the seeds ripen into a succulent mass (e.g. in cucumbers, melons, and gourds). In 

 Begoniact* also they project from the walls into the middle of the ovary, and 

 the latter looks in consequence as if it were divided into loculi. The androecium 

 exhibits great diversity. In some Cucurbitacese the five stamens are free; in 

 others they are partially united, and in a third group they are all completely fused 

 together into a column. In Begoniacese, also, the stamens are connate and form a 

 column. In many cases the anthers are sinuous, and in the genus (Cyclanthera) 

 there is a continuous anther all round the column. The Pepones are mainly tropical 

 plants. The Begoniacese grow especially in the tropical forests of America, where 

 they are not infrequently epiphytic. There is still some doubt as to the place of 

 origin of Melons, Gourds, and Cucumbers. The alliance is represented by the 

 Squirting Cucumber (Elaterium) in the South of Europe, and by Bryony 

 (Bryonia) in Central and Northern Europe. No fossil remains have been dis- 

 covered. The number of extant species hitherto identified is about 1100. 



Alliance LXIV. Cactales. 

 Families: Opuntiacece and Cactacece. 



Perennial plants, whose stems are much swollen or flattened. Flowers solitary; 

 actinomorphic or zygomorphic; hermaphrodite. The ovary consists of a hollow, 

 cup-shaped floral receptacle, from the inner waU of which spring filiform stalks 

 bearing the ovules (see fig. 209 * 2 , p. 77). The external surface of the receptacle 

 is clothed by floral -leaves arranged in a spiral; the lower leaves are small and 

 inconspicuous, the upper petaloid and brightly coloured (see figs. 441 * *> 3 > 4 > 5 ). Inside 

 the upper tubular prolongation of the receptacle are crowds of stamens arranged 

 spirally. The pollen is adhesive. The fruit is unilocular and succulent (see fig. 441 2 ). 

 The seeds contain no endosperm. 



The genus Pereskia alone exhibits thick, green foliage-leaves; in the other 



the leaves are replaced by small caducous scales or thorns, and assimilation 



:cted by means of the green cortical tissue of the swollen stems (see vol. i. 



pp. 327 and 440). The species of RhipuK, and Phyllocactus, which are epiphytic 



