BRYOPIIYTES 103 



The archegonia are developed as among the Marchantiales, with three 

 vertical intersecting walls, a cap cell, and a central cell which develops the 

 axial row. In this case the neck canal cells are six to eight in number. 



Sporophyte. — The sporophyte, even of Aneiira, is more complex 

 than that of Marchantia. Much more of the sporophyte is sterile tissue, 

 the sporogenous tissue being 'still more restricted. The sterile tissue 

 develops a foot and an elongated seta (fig. 231); and the spore output 

 is still further reduced by the development of elaters and by the use of 

 some of the sporogenous tissue in nourishing the functioning mother cells. 

 In certain forms there occurs also a mass of sterile tissue projecting into 

 the spore chamber from above (Aneura) or from below (Pellia), which, 

 on account of its relation to the elaters that radiate from it, is called 

 an elaterophore. As in Marchantia, the seta elongates with great rapidity 

 when the capsule is mature. The capsule opens usually by the longi- 

 tudinal splitting of the wall into four pieces (valves), which is a more defi- 

 nite and special mechanism for dehiscence than is developed among the 

 Marchantiales. 



Conclusions. — The anacrogynous Jungermanniales exhibit some of 

 the simplest gametophytes known among liverworts. There is a ten- 

 dency for the gametophyte to pass from the thallose state to the leafy 

 state, thus changing in form, but without any marked differentiation of 

 tissues. The sporophyte is more highly developed than among Mar- 

 chantiales, in the sense that there is more sterilization, more organization 

 of the sterile tissue, a stronger development of the seta, and a more spe- 

 cialized dehiscence. Apparently it is a group which has retained the 

 primitive structure of the gametophyte for a long time, but in which 

 the sporophyte has developed rapidly. In Pellia and Aneura, therefore, 

 we find the simplest gametophyte associated with an advanced sporo- 

 phyte, the converse being true of the Ricciaceae. 



(b) Acrogynae 



General character. — A good representative of the leafy liverworts 

 is Porella. As has been said, the Acrogynae are characterized not only 

 by being leafy forms, but chiefly by the fact that the apical cell of special 

 branches becomes an archegonium initial. This apical position of the 

 archegonium and hence of the sporophyte (fig. 235) is in sharp contrast 

 with their dorsal position among the Anacrogynae. 



Gametophyte. — In the development of the gametophyte there may 

 be three stages: (1) the filamentous stage, (2) perhaps the stage of an 



