II 



M USCINE^—HEPA TIC^—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), Xz; B-F, 

 development of the gemmae, Xs^s; G, an older gemma, X260; v, v' , 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 w^alls 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 



