1 66 



muscinea: 



thallus ; while in Oxymitra (Bisch.) they are raised above the surface. 



The sporange is a thin-walled spherical capsule, occasionally produced 

 under water, entirely filled with spores without 

 true elaters or columel, and, with its calypter, 

 depressed in the thallus. It is much less differ- 

 entiated in its structure than in the other 

 orders. In all the genera except Riccia and 

 Ox;ymitra the elaters are represented by sterile 

 cells among the spore-mother-cells. The spo- 

 range bursts irregularly when ripe, but the 

 spores are only set free by the decay of the 



Fig. 147. — Sphterocarpiis tetrestris Sm. Frond and archegone' 

 (magnified). 



Fig. 146. — Riella helicophyila 

 Mont, (magnified) 



Fig. 148. — Riccia. gla-uca L. A, section of apical region of 

 frond, ar, archegone ; c, oosphere ( x 50). B, immature 

 sporogonCj sg ; ar, neclc of archegone ( x 300). (After Hof- 

 meister.) 



surrounding tissue of the thallus. The spores of Sphsrocarpus (Mich.) 

 and Corsinia (Radd.) have a beautifully sculptured extine. Riella is 

 altogether dioecious, and perfects its fructification beneath the water. 



Principal genera : — Riccia (L.), Durisea (Bor.), Oxymitra (Bisch.), 

 Riella (Mont.), Sphaerocarpus (Mich.), Corsinia (Radd.). 



LlTERATURE. 



Kny— Pringsheim's Jahrb. wiss. Bot., 1866, p. 364. 

 Leitgeb — Die Riccieen, 1879. 



