146 



MOSSES AND FERNS 



CHAP. 



are periclinal, and for a short distance it is two-layered, as it is 

 permanently in Anthoceros ; but still further up it widens very 

 rapidly by the formation of repeated periclinal walls, and soon 

 comes to be much thicker than either the columella or the capsule 

 wall. A further study of the developing archesporium shows 

 that the divisions occur with a good deal of regularity. The 

 archesporial cells are divided by alternating vertical and trans- 

 verse walls into four layers of cells instead of two, as in Anthoceros, 

 and these cells are arranged in regularly placed 

 transverse rows. At first the cells appear alike, 

 but later there is a separation into sporogenous 

 and sterile cells as in AntJwceros. Each primary 

 transverse row of cells becomes divided into 

 two. The upper row grows much faster, and 

 its cells become swollen and the cytoplasm 

 more granular, while the lower row has its cells 

 remaining flattened and more transparent, i.e. 

 there is a separation of the archesporium into 

 alternate layers of sporogenous and sterile cells 

 as in A7ithoceros, but here the number of cells 

 is double that in the latter, and the longer axis 

 of the cells is transverse instead of vertical. In 

 the portion of the archesporium above the colu- 

 mella these alternate layers of spore mother 

 cells and sterile cells extend completely across 

 the cavity, and Leitgeb -^ has correctly figured 

 this, although he probably was mistaken in 

 assuming that this arrangement extended to the 

 base of the capsule. 



The further development of the capsule is 

 Fig. 73.— Longitudinal Hiuch like that of Anthoce7^os, but the division 

 section of a nearly of the chloroplast takcs place before the spore 



ripe sporogonium of '■ 



N. orbicularis, X50. mothcr cells are isolated, and the primary chloro- 

 plast is evident almost as soon as the sporogen- 

 ous cells are recognisable as such. The cells of the columella do 

 not become as elongated as in AntJwceros, and develop thicken- 

 ings much like those of the sterile cells of the archesporium, 

 and it was this partly that led Leitgeb - to the conclusion 

 that even where a definite columella was present it probably 

 arose as a secondary formation in the archesporium, similar 

 ^ Leitgeb (7), vol. v. PI. IV. Fig. 3a. ^ Leitgeb (7), vol. v. p. 50. 



