206 



MOSSES AND FERNS 



CHAP. 



It was found first that there was not the absolute constancy in 

 the number of cells given by him; thus in Fig. io8, A there 

 are only fourteen cells in the inner part of the endothecium, 

 and although there are sixteen cells in the outer row their 

 position is not perfectly symmetrical. Again the periclinal 

 division of the cells of the inner spore-sac takes place later than 

 he states is the case. 



In the eight primary cells of the amphlthecium there first 

 arise periclinal walls that divide each cell into an inner small 

 cell in contact with the endothecium, and an outer larger one. 



Fig. io8.— Three transverse sections of an older sporogonium of F. hygrometrica, X400; 



ar, archesporium; t, intercellular spaces. 



This first division separates the wall of the capsule from the 

 outer spore-sac. The latter next divides by radial and trans- 

 verse walls, and later by periclinal walls into two layers (Fig. 

 108). Almost coincident with the latter, the rows of cells 

 lying immediately outside it show a very characteristic appear- 

 ance. They cease to divide, and with the rapid growth in 

 diameter of the capsule become much extended both vertically 

 and laterally, but are compressed radially. It is between these 

 cells and the spore-sac that the characteristic air-space found 

 in the capsule is formed. This is first evident shortly after 

 the enlargement of the base of the capsule begins. The devel- 



