THE SALVINIACEyE. 



I. 





JiNCE all vegetation requires a cer- 

 tain amount of water for its 

 processes, it is not unusual for 

 various species of plants to be 

 found growing in swamps and 

 bogs, or even in lakes and ponds, 

 but cases in which plants have 

 entirely severed their connection 

 with the earth and tals-en to 

 floating on the surface of the 

 water are far less common. In 

 a survey of the vegetable kingdom, however, we find 

 that all the great groups have species or even whole 

 families that have adopted this mode of life. Among 

 the flowering-plants the little duckmeats {Lemnd) are 

 likely first to come to mind, but there is the great water 

 hyacinth (Piaropus), of Southern waters, and many 

 another, like the bladderworts, nearer home. Among 

 the liverworts various species of Riccia are found float- 

 ing, and even the ferns have provided an instance in that 

 remarkable floating fern, Ceratopteris thalictroides. It is 

 not surprising, then, to find a family of the fern allies 

 like the Salviniaceae committed to such an existence. 

 Indeed it is sometimes suggested that the Salviniace^ 



