MUSCINE& HEPATIC^ MARCHANTIALES 



45 



One of the surface cells of the bottom of the receptacle 

 projects as a papilla above the surface, and is cut off by a 

 transverse wall from the cell below. The outer cell next 

 divides again by a transverse wall into a lower cell, which 

 develops no further, and a terminal cell from which the gemma 

 is formed. This terminal cell first divides into two equal cells 

 by a cross-wall (Fig. 13, B), and in each of these cells a similar 

 wall arises, so that the young gemma consists of four nearly 



A. 



FIG. 13. Marchantia polymorpha. A, Plant with gemma cups (k, k), X2; B-F, 

 development of the gemmae, X525; G, an older gemma, X26o; v, v' t the two 

 growing points. 



equal superimposed cells (Fig. 13, D). The wall III in Fig. 

 13, D, arises a little later than wall II, and is always more or 

 less decidedly concave upward. Each of the four primary 

 cells of the gemma is divided into two by a central vertical wall, 

 and this is followed by periclinal walls in each of the resulting 

 cells. At first the gemma is but one cell in thickness, but 

 later walls are formed in the central cells parallel to the sur- 

 face, so that it becomes lenticular. As it grows older there 



