1921] HAUPT—REBOULIA 449 
With the development of the sporogenous tissue and the cells 
of the foot, the young sporophyte gradually assumes a dumb-bell 
Shape. The seta remains short throughout the entire history of 
the sporophyte. The calyptra, formed entirely from the venter 
of the archegonium, is 3-5 cells thick in this dumb-bell-like stage of 
the sporophyte. As development proceeds, the margins of the 
receptacle lobes grow up around the sporophyte to form a simple 
2-valved involucre. No perianth is developed, as in certain other 
genera of the Marchantiaceae. The receptacle stalk is very short 
at a stage in which the sporophytes are developed as far as has 
been described, and they pass the winter in this condition. 
Sporogenesis 
In the early spring, about the last week in March in the region 
where this material was collected, the receptacle stalk begins to 
elongate, and further development of the sporogenous tissue takes 
place. In the early spring the sporogenous cells give no indication 
of which are to form spore mother cells and which elaters (fig. 12), 
but by the first part of May the walls separating the protoplasts of 
the sporogenous tissue break down and form an abundance of 
mucilage, and the young spore mother cells and elaters are clearly 
differentiated (fig. 13). 
A striking feature of the sporogenesis of Reboulia is shown by 
the fact that the spore mother and elater primordial cells are derived 
from the undifferentiated sporogenous tissue by the same number 
of cell divisions. Thus an elater is not homologous with a row of 
spore mother cells, as in Marchantia, but with a single spore mother 
cell. Potentially sporogenous tissue is thus diverted to form elaters 
later than in Marchantia, and in this respect the sporophyte of 
Reboulia is primitive. 
With the breaking down of the sporogenous cell walls, the 
protoplasts of the young spore mother cells become withdrawn 
within the cell cavities and assume an amoeboid form, while those of 
the young elaters become elongated (fig. 13). This behavior was 
constant in all of the preparations examined, and in material 
collected in both of the localities in Illinois to which reference has 
been made. 
