THE PROBLEM 35 



to the water from the land, and altered their 

 structure accordingly. An extreme case is found 

 in the Duckweeds referred to in the first chapter, 

 plants which have lost almost all distinction 

 between leaf and stem, and are reduced to a 

 tiny frond which in Wolffia is even without 

 roots. The flowers, too, are extremely simple. 

 These minute water-weeds, which have lost all 

 resemblance to ordinary Flowering Plants, are 

 extremely successful and have spread over the 

 fresh waters of the whole world. By simplifying 

 their structure they have become able to com- 

 pete on equal terms with the fresh-water Algae, 

 and often to beat them in their own domain; 

 they have "stooped to conquer." Another fam- 

 ily of water Angiosperms, which has descended 

 to the level of lower plants, is that of the Podq- 

 stemaeeae, which flourish on rocks in the rushing 

 torrents and waterfalls of tropical streams. 

 They too have become completely transformed, 

 and have come to resemble anything but Flower- 

 ing Plants sometimes Mosses or Liverworts, 

 sometimes Lichens and sometimes Algae. In 

 the case of this family, there is thus a great 

 variety of forms, all alike strange and unfamiliar 

 among Angiosperms. 



In the sea alone the Angiosperms have met 

 with but little success. On our own coasts 

 we have our one marine Flowering Plant, the 



