II MUSCINE^— HEPATIC^— MARCHANTIALES 29 



continue to form for a long time, so that all stages may be met 

 with upon the same thallus. While both antheridia and arche- 

 gonia may be found together, in the two species R. glauca and 

 R. trichocarpa, mainly studied by myself, I found that as a rule 

 several of one sort or the other would be formed in succession, 

 and that not infrequently antheridia were quite wanting upon 

 plants that had borne numerous archegonia. Both archegonia 

 and antheridia arise from single superficial cells of the younger 

 dorsal segments of the initial cells. In their earliest stages 

 they are much alike, the mother cell of the antheridium being, 

 however, usually somewhat larger than that of the arche- 

 gonium. The cell enlarges and projects as a papilla above the 

 surface, when it is divided by a transverse wall into an outer 

 cell and an inner one. The latter divides but a few times and 

 forms the short stalk ; the outer cell, which has dense granular 

 contents, develops into the archegonium or antheridium as the 

 case may be. In the former case the divisions follow the 

 order already indicated for the typical Liverwort archegonium. 

 In the outer cell, which continues to enlarge rapidly, a nearly 

 vertical wall is formed (Fig. 2, C), which divides the cell into 

 two very unequal parts. This wall is curved and strikes the 

 periphery of the mother cell at about opposite points (Fig. 2, 

 G, i). A second wall of similar form is next formed in the 

 larger cell (G, 2), one end of which intersects the first wall, 

 and finally a third wall (3) intersecting both of the others is 

 formed. The young archegonium seen in vertical section at 

 this stage (Fig. 2, D) shows a large central cell bounded by 

 two smaller lateral ones; in cross-section the central one 

 appears triangular. Each of the four cells of which the arche- 

 gonium rudiment is now composed divides into two. The 

 outer ones each divide by radial walls into equal parts, and the 

 central one divides into an upper smaller cell (cover cell) and 

 a lower larger one (Fig. 3, E). The next divisions are hori- 

 zontal and divide the young archegonium into two tiers of cells. 

 The lower one forms the venter, and the upper one the neck, 

 and next the cover cell divides into four nearly equal cells by 

 intersecting vertical walls. The archegonium at this stage 

 (Fig. 2, F) is somewhat pear-shaped, being smaller at the 

 bottom than at the top, and the basal cell is still undivided. 

 It now rapidly increases in length by the transverse division 

 and growth of all its cells, and there is at the same time a 



