192 EVOLUTION OF PLANTS 
allied forms of the Old World, are the best-known 
examples of these arborescent lilies. 
Various other adaptations of the vegetative parts are 
shown by many Liliiflore. Most of them are herba- 
ceous forms, which develop underground stems capable 
of resisting extremes of both cold and dryness. These 
are either bulbs, tubers, or similar shortened and thick- 
ened subterranean stems in whose cells, or those of 
thick scale-leaves growing from them, are stored up 
starch and other food-materials. These bulbs and tubers 
can endure complete drying up without injury, and 
remain dormant during the long periods of cold or 
extreme drought to which the plant may be subjected, 
and start into growth very quickly on the advent of 
favorable growing conditions, drawing upon the stored 
reserve food until the new leaves and roots are de- 
veloped. 
These bulbous liliaceous plants are especially de- 
veloped in those countries which have a marked wet 
and dry season. California and the Cape district of 
Africa illustrate this, both of these regions being nota- 
bly rich in liliaceous plants, many of them having 
flowers of great beauty. 
The tendency to form zygomorphic flowers, found 
occasionally in the Liliifloree, becomes the rule in the 
two most specialized orders of the Monocotyledons, the 
Scitaminez, and the Gynandre. The former comprises 
the Ginger and Banana families, as well as the familiar 
Cannas of the gardens. The Gynandre include two 
families, of which the Orchid family is by far the more 
important, and includes a very large majority of the 
forms. Both Scitaminee and Gynandre are character- 
