Z t 6 SYSTEMATIC BOTANY. 



those with a free ovary, Malesherbiacese, Turneracese, and Passifloraceae 

 exhibit some points of agreement. They are natives of the warmer parts 

 of America ; but one occurs in Arabia and tropical Africa. They are 

 principally remarkable for their stinging hairs, which produce more 

 violent irritation than our indigenous Nettles. Mcntzelia hispida has a 

 purgative root. Loasa, Bartonia, &c. are often cultivated on account of 

 the beauty of their flowers ; but some of them are rendered less valuable 

 by their stinging-property. 



CACTACEJE (INDIAN FIGS) are fleshy and thickened, mostly leafless 

 plants, of peculiar aspect, globular or columnar and many-angled, or 

 flattened and jointed, usually with prickles. Flowers solitary, sessile ; 

 the calyx and corolla sometimes 4-merous, but generally undistinguishable 

 and imbricated in several spiral cycles adherent to the 1-celled ovary ; 

 stamens indefinite ; placentas parietal ; fruit succulent ; seeds numerous, 

 parietal or in the pulp, aperispermic. 



ILLUSTRATIVE GENERA. 



Tribe 1. ECHINOCACTEJB. Floicer- 

 tube prolonged beyond the ovary. 

 Stem tubercled or spiny, rarely leafy. 



Mammillaria, Haw. 



Echinocactus, Link et Ott. 



Cere us, Haw. 



Tribe 2. OPUNTIEJE. Flower- 

 tube not prolonged beyond the ovary. 

 Stem branched, jointed. 



Rhipsalis, Gcertn. 



Opuntia, Tournef. 



Pereskia, Plum. 



Affinities, &c. These plants are generally distinguishable at first sight 

 by the remarkable forms of their succulent stems and the absence of true 

 leaves; but this anomalous condition of the stem is not a decisive charac- 

 ter, nor does it even carry with it indications of affinity, since we find it 

 among Euphorbiaceoe, in StapeliecB among- the Asclepiadaceae, in Vitacese, 

 and elsewhere. The ordinary forms scarcely require description ; but it 

 must be noticed that the leaf-like structures of Epiphyttum <fcc. are flat- 

 tened branches, and the leaves are represented solely by spines in the 

 common kinds, each tuft of spines representing an abortive shoot with 

 undeveloped internodes ; Pereskia, however, bears true leaves, sessile or 

 stalked. The stems have a woody axis of the normal Dicotyledonous 

 structure : the chief mass of the stem of the phylloid kinds is made up of 

 the greatly developed cortical parenchyma; but the globular and columnar 

 kinds are very solid : the wood is remarkable for a peculiarly formed spiral 

 thickening of its cells ; and the parenchyma of old stems is densely loaded 

 with crystals of calcium oxalate. 



The relations, as founded on the structure of the flowers, are, perhaps, 

 closest with Loasaceae, and beyond them with the Cucurbitaceae, with, 

 however, many important points of difference from the last. There is a 

 considerable resemblance in certain respects to Mesembryanthaceae ; for the 

 placentas of that Order and those of the present are apparently but slight 

 modifications of a similar fundamental structure. Some degree of affinity 

 exists between Cactacese and Ribesiaceae ; but the dicarpellary structure 

 there and the perispermic seeds are important distinctions, and indicate 

 a closer relationship of the latter plants to Saxifragaceae. 



