PRINCIPAL GROUPS OF PLANTS. 95 



and Botrychium belong, develops a subterranean prothallus which 

 is destitute of chlorophyll. The prothallus is in some cases tube- 



FIG. 59. Marsilea quadrifolia (from Bantam Lake, Conn.), a submersed or emersed 

 aquatic plant belonging to the Marsileaceae, a family of the Pteridophytes. Of the forty 

 different species, only two or three are found in the United States. It produces long, slender 

 rhizomes, which are buried in the muddy bottoms of shallow lakes or streams and from 

 which arise the leaflets which float on the surface. The leaves are on long, slender petioles 

 and 4-foliate, the leaflets being mostly triangular-obovate. In Marsilea quadrifolia, a 

 European form growing in Connecticut and Massachusetts and frequently cultivated, the 

 leaves are nearly glabrous, while in M. vestita, a form found in shallow ditches in the 

 Southern States, the leaflets are usually hairy. This character is quite marked in the spor-' 

 ocarps of the two plants. After a photograph by Henry Troth. 



