750 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



UrtieaceEB also the perianth persists as a similar investment (e.g. Morus). In 

 Amaranthaceae the pedicels are furnished with bracts which resemble the perianth- 

 segments and, like them, envelop the fruit. In those Centrospermge which are 

 destitute of floral-leaves (achlamydeous), e.g. the Piperacese, the floral envelopes are 

 replaced by bracts. The Caryophyllacese have distinct calyx and corolla, and are 

 often placed in the sub-class Polypetalse; they have, however, decided afiinities with 

 the CentrospermEe. The andrcecium is composed of one whorl in Urticacese and 

 Chenopodiacese, and of two whorls in most of the other families. The filaments are 

 inflexed in the bud in Urticaceae, but spring up when the perianth opens and so 

 eject the pollen from the anthers (see p. 306). Most of the Centrospermse have 

 dust-like pollen, but in Caryophyllacese and Nyctaginacese the pollen is adhesive. 

 In Urticaceae and in some Caryophyllaceae the embryo is erect, in the rest it is 

 horse-shoe shaped or spirally curved (see fig. 425^). The copious farinaceous 

 endosperm of some Polygonaceae and Chenopodiacese (Polygonum Fagopyrum, 

 P. Tataricum, Ghenopodium Quinoa) is used for fiour. The Centrospermse are 

 distributed in every quarter of the globe. The Piperacese, Urticaceae, PolygonaceEe, 

 Amaranthaceae, and Nyctaginaceae are developed in the greatest variety in the 

 tropics. Most Centrospermae, however, are found in the temperate zones. The 

 Mediterranean Flora is especially rich in Caryophyllacese, whilst Equatorial America 

 abounds particularly in Amaranthaceae and Nyctaginaceae. The Polygonaceae grow 

 chiefly on the banks of streams; the Chenopodiaceae are very prevalent by the 

 sea-shore and on salt steppes, especially in Central Asia. Several Caryophyllaceee 

 flourish also on the confines of perpetual snow. Silene acaulis (see Plate XII.) is 

 one of the most remote outposts of the Phanerogamia and has been met with in 

 Franz Joseph's Land at 81° north latitude, and in the Central Alps at a height of 

 3160 metres above the sea-level. Fossil remains of Urticaceas and Piperaceas have 

 been recognized in the deposits of the Mesozoic and Tertiary periods. The number 

 of species now living amounts to about 4200. 



Alliance XXXVI.— Proteales. 



Family: Proteaceoe. 



Perennial herbs, with underground stems which project but little above the 

 earth, or herbs and small trees with entire or variously lobed and incised stiff 

 foliage-leaves without stipules. Flowers in capitula or spikes (see fig. 426 ^y, actino- 

 morphic or zygomorphic, hermaphrodite, pseudo- hermaphrodite, monoecious and 

 dioecious. Perianth 4-partite, petaloid; the four segments are connate at the base, 

 and, in the bud, have their free ends closed together like valves (see fig. 426 ^). 

 Ovary superior, free, unilocular. Number of ovules one to many. Placentation 

 parietal. Each ovule has a double integument; the micropyle is directed towards 

 the base of the ovary. The latter is surrounded by tissues which secrete honey. 

 The number of stamens is equal to that of the perianth segments; the short filament 

 is adnate to the perianth-segment behind it (see fig. 426 '). Fruit a drupe, a nut, 



