ANGIOSPERM^E 



393 



ponds, and at the South 



has become naturalized, 



and in some places causes 



much trouble by the ra- 

 pidity with which it has 



increased. The flowers 



are strongly zygoinorphic, 



and in Pontederia cordata 



are trimorphic, i.e. there 



are three different lengths 



of styles and stamens. 

 Bromeliaceae. The 



Bromeliaceas are exclu- 

 sively American, and espe- 

 cially developed in the 



tropics of South America 



and the West Indies. A 



few species of Tillandsia, 



among them the familiar 



"Spanish-moss" (T. us- 



neoides'), represent the 



family in the United 



States. The flowers, struc- 

 turally, are much like 



those of the true Lilies. 



They are often in spikes, 



the flowers in the axils 



of showy pink or scarlet 



bracts. With few excep- 

 tions they are epiphytes, 



and are a conspicuous 



feature of the flora of 



tropical America. The 



leaves are long and slender, often crowded together at the base of the plant 



(Fig. 371), where their expanded 

 bases serve as reservoirs of moisture, 

 and accumulate, also, dust and 

 humus. Upon the surface of the 

 leaves are scurfy scales, which also 

 serve to catch water. The Pineapple 

 (Ananas saliva) is the most familiar 

 member of the family. The fruit, 

 here, is an aggregation of enlarged 

 flowers, attached to the juicy floral 

 axis the whole structure is much 

 like a gigantic mulberry. 



The roots in these plants serve 

 mainly as organs of attachment, and 

 may be quite absent. 



FIG. 368. Iris xiphium (X J). (After BAILEY.) 



FIG. 369. Tradescantia Virginica. A, 

 inflorescence, reduced. B, pistil. C, 

 stamen, enlarged, showing the staminal 

 hairs. 



Order IX. Scitamineae 



The Scitaminese are, with very 

 few exceptions, tropical plants, fre- 



