Benedict : The genus Ceratopteris 465 



contains not only the several species included here, but probably 

 several more, which further collections and field work will bring 

 more clearly to light. 



The principal difficulty that arose was due to the lack of 

 complete series of the different forms through which the leaves pass 

 in their seasonal development. The conditions seem somewhat 

 analogous to those which exist in such plants as Campanula 

 rotundifolia, etc., in which the juvenile leaves are often more dis- 

 tinctive than the later growth but may have disappeared before 

 these develop. Thus a large proportion of the material studied 

 represents only the mature sporophyls which, although necessary 

 in determining the sporangial characters, may yet leave the exact 

 identity of the specimen very much in doubt. 



A knowledge of the ecology of the various forms would also 

 assist greatly in their classification. The evidence of this sort at 

 hand indicates that some of the plants occupy very different hab- 

 itats. They have been found growing in merely damp soil, float- 

 ing or submerged in water which may be running or stagnant, 

 fresh or brackish, at sea-level and up to two thousand feet alti- 

 tude. All seem to require at least wet soil, and it is not unlikely 

 that all are accustomed to temporary if not continuous submerg- 

 ence, during which the young vegetatively formed plants are 

 borne floating until stranded in some situation favorable to further 

 growth. 



The genus (and the monotypic family Ceratopteridaceae *) may 

 be described as follows : 



Aquatic or semi-aquatic plants of tropical or subtropical regions. 

 Stem creeping or ascending, reduced, sparsely scaly. Roots borne 

 on the stipes. Leaves alternate, successive, viviparous, soft-her- 

 baceous, dimorphic, the venation reticulate, without included vein- 

 lets, the stipes in some species horizontal at first, then bent abruptly 

 upwards, bearing the roots on the horizontal parts. Sterile leaves 

 erect or spreading, floating in some cases, 2-4 times pinnately or 

 subternately divided. Sporophyls taller, erect, 2-5 times divided, 

 the ultimate segments linear, with the margins narrowly and evenly 

 revolute, often meeting along the midvein, covering two or three 

 rows of areolae. Sporangia abaxial, scattered in one or two lines 

 along the longitudinal veinlets, and protected at first by the re- 

 flexed margins, thin-walled, sessile, globose, the wall-cells sinuate, 



* Underwood, Our Native Ferns 78. 1900. [Ed. 6.] 



