ANGIOSPERM^, DICOTYLEDONES. 



787 



on the branches of old trees, have much-branched and segmented phylloclades, 

 which often hang in curves; the segments of the stem in Opuntias are laterally 

 compressed, and more or less discoid (see vol. i. Plate IV.). The cylindrical stems 

 of the Queen of Night (Cereus nycticalus, vol. i. Plate VII., in foreground) are 

 prismatic, and climb up rocks and the bark of trees by means of clinging roots. 

 Other species of Cereus, such as Cereus giganteus, which grows to a height of 

 20 metres, possess erect columnar stems (Plate VII., left hand, middle distance). 

 Another set of Cereus-species, including the many forms of Mamillaria, Melocactus, 

 Echinocactus, and Echinojpsis, are spherical or truncate; they are covered either 

 with papillae, each of which is crowned by a bunch of prickles (see fig. 441 ^), or 



Fig. 441.— Cactacese. 



1 Flower. 2 Fruit of Cereus giganteus. s Mamillaria pectinata. * Cereus dasyacanthus. ^ Bchinocactus horizontalis. All the 

 flgm-es reduced. 



with tubercles, whicli coalesce into crests and ribs (see figs. 441 * and 441 ^). The 

 Cactuses are natives of the New World, and inhabit regions where a short, rainy 

 season is followed by a prolonged period of drought. The largest number of species 

 is found in Mexico. Some species also occur at high elevations in the Andes. 

 No fossil remains are known. The number of species ascertained to exist at the 

 present time is about 1300 



Alliance LXV. — Picoidales. 



Families: Portulacece, Molluginacece, Ficoidacece, Mesemhryanthemacece. 



Annual and perennial herbs and under-shrubs, with entire fleshy foliage-leaves. 

 Flowers solitary or in fascicles and glomerules; actinomorphic, hermaphrodite. 

 The floral -leaves free or else connate at the base; in one, two, or several 2-5- 

 merous whorls. Either all the floral-leaves, or only those of the lowest whorl, 

 are sepaloid; in the latter case, the upper whorl or whorls are petaloid. The 



