CRYPTOGAMS 



451 



The macro- and microsporangia do not develop, like those of the Filices, on the 

 under side of the leaves, but are enclosed in special receptacles at their base, 

 constituting sporangial fructifications or sporocarps. The wall of the sporangium, 

 which consists of a single layer of cells, has no annulus. 



The Water-Ferns are divided into two families : Marsiliaccae, including three 

 genera, and Salviniaceac, with two genera. 



Marsiliaceae. To this family belongs the genus Marsilia, comprising about 

 fifty species, of which M. qiiadrifoliata (Fig. 413) may be taken as an example. 

 This species grows in marshy meadows, and has a slender, creeping, branched axis, 

 bearing at intervals single leaves. Each leaf has a long erect petiole, surmounted 

 by a compound lamina composed of two pairs of leaflets inserted in close proximity. 



Kl<:. 413. Miirsili" iiucilrifuliatn. <', 

 Young leaf; .-. sponK-irps. (Att<-i 

 BISCHOFK, reduced.) 



Fn;. 414. I'iltdariu gloltidifera . .-, .Sjxjro- 

 ;carp. (After BISCHOFF, reduced.) 



The stalked oval s]x>rocarps (s) are formed in pairs above the base of the leaf-stalk, 

 or in other species they are more numerous. Each of them corresponds in develop- 

 ment to the quadripinnate sterile lamina, but is not divided into pinnae. The 

 sori of sporangia are enclosed within the capsule, disposed in two rows in 

 correspondingly arranged cavities ; in the young fruit each chamber opens outwards 

 on the ventral side by means of a narrow canal, which eventually becomes closed. 

 The sporangia are developed originally, as in other ferns, from superficial cells, but 

 become arched over by the surrounding tissue, and thus subsequently appear as 

 if formed in internal chambers. As Fig. 413 shows, the young leaves, the develop- 

 ment of which is as in the Filices, are circinate. 



Pilularia also grows in bogs and marshes. It differs from Jfursilia in its 



