SECT. II 



PHANEKOGAMIA 



527 



distinctively characteristic of this family alone, as some of the Euphor- 

 biaceae and Asclepiadaceae possess a similar habit. 



Geographical Distribution. — The large family of the Cadaceae is restricted 

 to the warmer countries of America. Like most succulents, the plants of this 

 group are typically xerophilous, although they occasionally occur as epiphytes 

 on the dry bark of trees in damp forests. They attain their greatest development 

 in the dry regions in the south-western part of North America, where the columns 

 of the Monument Cactus, Cereus giganteus, with their candelabra-like branches, 

 tower 20 m. high above the naked, rocky soil. They are especially prevalent 

 in the high table-lands of Mexico, and, extending almost to the snow-line, exhibit 

 the most astonishing diversity of form. One species, Opimtia ficus indica, with 

 edible berries, has escaped from cultivation in the neighbourhood of the Medi- 

 terranean, and, like the American Agave, has become so common that it is now 

 a characteristic plant of that region. It is on this plant that the Cochineal 

 insect is cultivated. The Cadaceae are largely cultivated as hot- house and window 

 plants. 



Order 10. Columniferae 



Flowers hypogynous, hermaphrodite, actinomorphic, with valvate 

 calyx and pentamerous perianth ; stamens usually MONADELPHOUS, 

 although typically five in number, becoming INDEFINITE by division ; 

 carpels 2 — <x> ; ovary syncarpous, septate, corresponding to the 

 number of carpels. 



The andrcecium, in particular, is characteristic of the Columniferae. 

 In some forms it is constructed, according to the Dicotyledonous type, 

 of two pentamerous whorls ; but in the majority of cases one whorl, 

 usually the episepalous, is suppressed or replaced by staminodia, 

 while the other, in consequence of the division of the staminal rudi- 

 ments, consists of a larger number of members. In addition, the 

 filaments of the stamens in most Columniferae are united into a longer 

 or shorter column, or, more appropriately described, into a tube, 

 whose derivation from the five or ten original 

 rudiments is only recognisable after investiga- 

 tion of its mode of development and a comparison 

 with allied forms. A division of the carpels, 

 similar to that of the stamens, is also of frequent 

 occurrence in the gynoecium. 



Family Tiliaeeae. — Sepals eree; petals 

 VALVATE in the bud ; stamens usually numer- 

 ous, free ; anthers introese, dithecious ; 

 pollen-grains not spiny (Figs. 492, 493). 



The Tiliaeeae are for the most part woody 

 plants, with toothed or lobed stipulate leaves. 

 The flowers, which are adapted to insect-pollination, are united in 

 clusters, and produce a dry capsule or an indehiscent fruit. 



The andrcecium consists in some species of two pentamerous whorls, thus 

 representing the primitive type from which the more complicated andrceeia of 



Pra. 492.— Tiliaeeae. 

 diagram (Tilia). 

 Eichler.) 



Floral 

 (After 



