190 FAMILIES OF FLOWERING PLANTS 
Western prickly pear (Opuntia humifusa ). After Britt. & Brown Ill. Fl. North- 
east U. S. 
Indica, which now occurs throughout Southern Europe, is the food plant 
of the cochineal insect. Our own native Opuntias are highly ornamental 
in the dry fields and rocky ledges when covered in early summer with a 
mass of yellow flowers. The genus Echinocactus is noted for its very 
formidable hooked spines; while Cactus (Mamillaria), a genus in which 
the plants are of small size and the flowers of bright colors, is particu- 
larly desirable in pot cultivation. 
The order MyrtirLoraz, or MyrraEs, may be known by the gamo- 
sepalous calyx, the sepals being joined together, and by the compound 
ovary, to which the calyx is usually adnate. There are 16 families, of 
which the most important are the Thymelaeaceae, Lythraceae, Rhizo- 
phoraceae, Combretaceae, Myrtaceae, Melastomaceae and Onagraceae. 
Family Geissolomaceae. Geissoloma Family. Consists of a single 
genus, Geissoloma, confined to the Cape of Good Hope. They are low 
shrubs of no particular interest. 
Family Penaeaceae. Consists of about 5 genera and 20 species, 
also natives of South Africa. The parts of the flower are in fours, and 
‘the ovary affords an exception to the usual rule in the order, in that it 
is superior to, or free from, the calyx. 
Family Oliniaceae. Olinia Family. Another family with a single 
genus, native of the sdme region. 
Family Thymelaeaceae. Mezereon Family. ‘Shrubs or trees with 
peculiarly tough inner bark. They have entire leaves, and flowers with — 
