BRYOPHYTA. 



697 



contractile. They assist in the dispersal of the dust-like spores in many cases, 

 though the details of their co-operation in this respect is not always the same. 

 Before the ripening of the spores the elaters play an important part in the nutrition 

 of the spores; they are sterile cells or filaments intermixed with the spores to which 

 they conduct food-substances during their development. Attention has been 

 already drawn to the brood-bodies or thallidia of Liverworts (c/. p. 24). 



Ricciacece. — These are very simple little forms occurring in wet places or floating 

 in water (Riccia natans) like a Duckweed. The thallus is lobed or it may be 

 ribbon-like and branched. The sexual organs are sunk in little chambers on the 

 upper surface of the thallus; antheridia and archegonia may occur on the same or 

 on different individuals. The fertilized egg-cell is here entirely converted into a 

 spore-capsule, i.e. a sheath inclosing spores. No elaters are present in this family, 



Fig. 395. 



1 Vertical section through an air-chamber of the Liverwort Slarchantia polymorpha showing the stomate-like pore and the 

 assimilating filaments. '■' Transverse section of a leaf of a Moss, Barbula aloides, showing the projecting plates of cells. 

 1x300; 2x380. 



nor is there a sterile base or foot. The genus Riccia includes 107 species; there are 

 110 species in the whole family. 



Marchantiacece. — The oophyte is a lobed band-like thallus (c/. fig. 196 \ p. 23) 

 with marked dorsi-ventrality. On the upper surface are a number of chambers each 

 opening to the exterior by a single stomate-like pore {Marchantia, fig. 395^). These 

 chambers are really excavations of the upper surface which become closed in 

 save for the pores in question. From the floor of each chamber sprout filaments of 

 chlorophyll-containing cells (fig. 395^); these form the main assimilating tissue of 

 the thallus. In Marchantia and Lunularia brood-bodies (or gemmse) are budded 

 off" in cup-like receptacles (c/. fig. 196 ^ p. 23). The sexual organs in this family are 

 borne on special receptacles on the upper surface of the thallus. These may be 

 either shield-like or stalked and umbrella-like (as in Marchantia, Fegatella, &c.). 

 The male and female organs respectively occur on separate receptacles and are 

 variously arranged. There are special sheathing structures associated with the 

 archegonia. The sporophyte generation or sporogonium has a sterile base or foot 

 which remains embedded in the archegonium. The spore-capsule is joined to the 

 foot by a narrow, isthmus-like neck. The capsule opens by splitting into teeth. 

 Elaters are present. Considerable variety is shown in this famil}^ in the form of the 

 receptacles of the sexual organs. 



165 species have been distinguished. 



