194 EVOLUTION OF PLANTS 
the New World, is the Bromeliacee. These are char- 
acterized by modifications of the vegetative parts rather 
than by the flowers, which are rather simple in structure. 
Most of the order are epiphytes, and they form one of 
the most striking features of the tropical American flora. 
The best known of these are the so-called “Spanish 
Wie. 47 siiomeaouy eden) Scitamines, Orchidacex).— A, flower of Canna: 
the flower is strongly zygomorphic, with inferior ovary, 0, and the 
stamens reduced to a single one; B, the single stamen, an, and the 
upper part of the pistil, st, of A; C, flower of an orchid (Arethusa), 
showing the marked zygomorphy, inferior ovary, 0, and the ‘‘lip,” J; 
D, a section through the ‘‘column,”’ or coherent stamen and pistil of 
Arethusa, showing the single anther, an, and the stigma, st: the rela- 
tive positions of the anther and the stigma are such that insect-pollina- 
tion is absolutely necessary ; E, flower of the wild yellow peste ed 
(Cypripedium pubescens), one of the orchids; /, the sac-shaped lip; 
F, the column of the lady’s-slipper, showing one of the two fertile sta- 
mens, an, the stigma, st, and the third, sterile stamen, «. 
moss,” of the southeastern United States (Tillandsia 
usneoides), and the cultivated pineapple. Several spe- 
cies occur in Florida, but it is further south that they 
reach their greatest development. In the West Indies 
they are abundant and varied, and form a very conspic- 
uous feature of the vegetation, covering the branches of 
