BRTOPHTTA. 



697 



contractile. They assist in the dispereal of the dust-Hke 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 elatei-s 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 (cf. p. 24). 



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

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

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

 upper surfauje of the thaUus; antheridia and archegonia may occur on the same or 

 on diflerent individuals. The fertilized egg-cell is here entirely con\erted into a 

 spore-capsule, i.e. a sheath inclosing spores. Xo elaters ai-e present in this family. 



Kg. sss. 



1 Tatical sectioD tbrou^ &n air-chamber of Uie liverwort Jfar^'.^.Tf.fja poli/morpha showing tie 5ton::ite-Iike pore and the 

 asamOatii^ filaments. ^ Trausreise section of a leaf of a Mosa, Barbuia a'i:ijes, showlcc the projecting i:l:3ites of cells. 



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

 110 species in the whole family. 



Marckantiacca. — The oophyte is a lobed band-Kke thaUus (cf. tig. 196 ^, p. i-S'i 

 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 thaUus. In Jlaixhantia and Lunulai-ia brood-bodies ^or gemmse) are budded 

 off in eup-Kke receptacles {cf. fig. 196\ p. 23). The sexual organs in this family are 

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

 either shield-Uke or stalked and umbreUa-like (^as in Marchantia, FegatcUa, kc,}. 

 The male and female origans respectivelv occur on sepai^ate recenaeles and are 

 variously arranged. There are special sheathiniT structures associated with the 

 aichegonia. The sporophyre generation or sporogonium has a sieriie base or foot 

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

 foc<t by a narrow, isthmns-Iike neck. The capsule opeus by splitting into teeth. 

 Elaters are present. Ckinsiderable variety is shown in this famiiy in the form of the 

 leceptad^ of the sexnal organs. 



165 species have been distinguished. 



