PTERIDOPIIYTES 



171 



Salviniaceae 



These are the floating ferns, comprising two genera, Salvinia and 

 Azolla, with few species, but some of them are widely distributed. 



Sporophyte. — The sporophyte 

 body is a floating, dorsiventral stem, 

 that develops by an apical cell with 

 two cutting faces, instead of the apical 

 cell with three cutting faces usual 

 among ferns. The segments are cut 

 off right and left, and subsequent 

 divisions result in eight rows of cells, 

 four ventral and four dorsal. In 

 Salvinia (fig. 396) the dorsal rows of 

 cells give rise to four rows of broad, 

 flat, overlapping, aerial leaves; while 

 the two central ventral rows give rise 

 to submerged and much dissected 

 leaves that bear the sporangia. The 

 two lateral ventral rows give rise to 

 the branches, and roots are entirely 

 lacking. In Azolla the two central 

 dorsal rows of cells do not give 



• i 1 i I u u i iU Fig. ?q6. — Salvinia, showing the 



nse to lateral members, but the , , „ \. , j ,u j- . j 



' broad floating leaves, and the dissected 



two lateral dorsal rows produce submerged leaves bearing sporocarps. 



leaves which arc dorsiventrally lobed 



(fig. 397). The submerged 

 ventral lobes bear the spo- 

 rangia, and a chamber in the 

 aerial dorsal lobe is inhab- 

 ited by an endophytic alga 

 (Anabaena) . The two central 

 ventral rows produce roots, 

 and the two lateral ventral 

 rows produce branches. 

 Sporocarp. — The sporangia 

 Figs. 397, sgS. — Azolla: 397, ventral surface are submerged, as described, 



of branch, showing leaves and =P°roc^ps; ^^^ ^^^^ ^^^^ .^ completely 



invested by the indusium, 



398, megasporocarp and microsporocarp. 

 Campbell. 



