PTERIDOPHYTES 
17! 
Salmniaceae 
These are the floating ferns, comprising two genera, Salmnia 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 
Salmnia (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 
Fra * 
Salvinia, showing the 
rise to lateral members but the ra * 39 avna, sowng 
- rS ' l ' broad floating leaves, and the dissected 
two lateral dorsal rows produce submerged kaves bearing sporocarps. 
leaves which are 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, 398. Azolla: 397, ventral Burface are submerged, as described, 
of branch, showing leaves and sporocarps; , , . 1*1 
SgS.megasporocarpand nncrosporocai.--^ and each SOrUS 1S Completely 
CAMPBELL. invested by the indusium, 
