FILICINEM. 
453 
latter is cup-shaped and therefore open at the apex, whereas the wall of the former 
completely encloses the sorus, as does the indusium of Cyathea. The sporocarp 
of the Salviniacese is then a sorus, the term being used in the sense in which it is 
applied to the fructification of Ferns, but here the indusium is much more fully 
developed, consisting of two layers of cells, the walls of which, toward the upper 
part of the capsule, become lignified in AzoUa. 
Each sporocarp contains either microsporangia or macrosporangia, but both 
kinds of sporocarp occur in the same plart and even upon the same leaf, so 
Fig. ^Tg.—Salvim'a na/ans ; A transverse section of a stem bearing a whorl of leaves, / aerial leaves, iv submerged leaf with 
several teeth, ysporocarps on it (natural size) ; B longitudinal section through three fertile teeth of a submerged leaf, a a sporo- 
carp with macrosporangia, i i two sporocarps with microsporangia ; C transverse section of a sporocarp with microsporangia 
7ni; D transverse section of an aerial leaf, hti hairs of the under side, ho hairs of the upper side, fp epidermis, I air-cavities, the 
dark ones show the vertical walls of the tissue in the background {B — D X lo) ; E cells of a lamella of tissue in the leaf; F one of 
the cells after contraction of the contents in glycerine. 
that the plant is monoecious. The microsporangia are contained in Azolla, as 
in Salvima, in large numbers within the sporocarp; in Azolla only a single 
macrosporangium is formed in a sporocarp, whereas in Salvinia several macro- 
sporangia are formed. All the spores derived from the mother-cells (i6) in a 
microsporangium reach maturity, but only one of the (4X i6) spores of a macro- 
sporangium ever becomes ripe, so that in Azolla, where there is but one macro- 
sporangium in a sporocarp, a single macrospore is enclosed by the wall of the 
