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 Liliiflorse. 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 Liliiflorse, becomes the rule in the 

 two most specialized orders of the Monocotyledons, the 

 Scitaminese, and the Gynandrse. The former comprises 

 the Ginger and Banana families, as well as the familiar 

 Cannas of the gardens. The Gynandrse include two 

 families, of which the Orchid family is by far the more 

 important, and includes a very large majority of the 

 forms. Both Scitaminese and Gynandrre are character- 



