BRYOPHYTES 



99 



special structure (receptacles). In some cases the receptacles are sessile, 

 but in Marchantia they become long-stalked, the archegonial and an- 

 theridial receptacles occurring on different gametophytes. 



The receptacle borne by the antheridial branch is a disk with 

 lobed margin, a growing point being at the tip of each lobe (fig. 

 228). Over the upper surface of this disk the antheridia occur in 

 flask-shaped cavities formed by the overgrowth of the adjacent tissue. 

 From the bottom of each cavity a single antheridium arises (rarely 

 two), similar in structure to those described under Ricciaceae (figs. 

 205-210). 



The receptacle borne by the archegonial branch is star-shaped (fig. 

 229), the archegonia occurring in the notches between the rays, in con- 

 nection with the growing points. They arise from the upper surface 



Figs. 228, 229.- 

 cupule; 229, 



Marchantia : 228, thallus bearing antheridial branches and a 

 larger thallus bearing archegonial branches and a cupule. 



(morphologically) of the disk, but as this becomes the apparent lower 

 surface by the overgrowth of the upper surface, they hang within the 

 notches neck downward. They develop as in the Ricciaceae, but there 

 are usually eight neck canal cells (figs. 212-219). 



Sporophyte. — The sporophyte begins to develop as among the Ric- 

 ciaceae, but not all of the cells of the endothecium produce sporogenous 

 tissue. Approximately half of these cells give rise to the sporogenous 

 tissue and spores. This means that the sporogenous tissue in the sporo- 

 phyte of Marchantia is reduced as compared with that of the Ric- 

 ciaceae. The remaining tissue of the endothecium, since it does not 



