666 



FAMILIES OF ANGIOSPERMS. 



the labellum stands one of the sepals more showy than the others, the 

 "banner." The two lateral "strings" of the slipper are the two other 

 petals. The stamens are still more reduced in some other genera, while 

 in several tropical orchids three normal stamens are present. 



There are thus four striking modifications of the orchid flower: ist, the 

 flower is irregular (the parts of a set are different in size and shape); 2d, 

 adnation of all parts with the pistil; 3d, reduction and suppression of the 

 stamens; 4th, the ovary is twisted half-way around so that the posterior 



Fig. 553- 



Diagrams of orchid flowers. A , the usual 

 type; B, of cypripedium. (Vines.) 



Fig. 554- 



Diagram of flower 

 of canna. 



side of the flower becomes anterior. Floral diagrams in fig. 553 show 

 the position of the stamens in two distinct types. The number of orchid 

 species is very large, and the majority are found in tropical countries. 



Related to the orchids are the iris family, in which the stigma is expanded 

 into the form of a petal, and the canna family. In the canna the flower 

 is irregular (see figs. 470, 471) and the ovary is inferior. (See Chapter 

 XLIII, on pollination, for description of the canna flower.) 



