io6 



MOSSES AND FERNS " 



CHAP. 



tion (Fig. 53, A), which separate a central cell, nearly tetra- 

 hedral in form, from two outer cells. In the complete separa- 

 tion of the central cell by these first two walls, Porella appears 

 to dififer from the other Jungermanniaceae examined, (Leitgeb 

 (7), ii., p. 44), where these first two peripheral cells do not 

 reach to the top of the antheridium, and a third cell is cut off 

 before the separation of the central part of the antheridium 

 from the wall is complete. It is possible, too, that in Porella 

 this may be sometimes the case. The antheridium in cross- 

 section at this stage shows two perfectly symmetrical halves 



Fig. i3. — Porella Bolanderi. A, B, Cross-sections of young antheridia, X600; 

 C, longitudinal section of nearly ripe antheridium, Xioo; D, ripe antheridium in 

 the act of opening, X50; E, F, spermatozoids, X1200. 



(Fig. S3, A). The two central cells form a rhomboid sur- 

 rounded by six cells, the first of the primary peripheral cells 

 being in each case divided into two. The divisions proceed 

 rapidly in both the central cells and in the peripheral ones. In 

 the latter they are for a long time always radial, so that the wall 

 remains but one cell thick ; but as the antheridium approaches 

 maturity periclinal walls also form in the lower part, which 

 thus becomes double, and at places even three cells thick. 

 After the division of each primary central cell into equal 



