152 



MOSSES AND FERNS 



CHAP. 



stages at least, a similar columella will be found. The single 

 embryo that Leitgeb (1. c. PL IV., Fig. yy) figures of N. orbi- 

 cularis (valvata) is at once seen to be abnormal, and as his con- 

 clusions were drawn from a study of similar dead embryos in 

 the other species, they cannot be accepted without more satis- 

 factory evidence. While in the main corresponding to the em- 

 bryo of Anthoceros there are some interesting differences which 

 are closely associated with the structure of the older sporogo- 

 nium. The foot is smaller than in Anthoceros and derived only 

 from the lowest tier of cells. The columella is decidely smaller, 

 and the archesporium, as well as the young sporogonium wall, 

 relatively much thicker. As in Anthoceros, the archesporium 

 does not extend to the foot, but is separated by the zone of 



B 



Fig. 83. — Notothylas orbicularis. A, Four-celled embryo; B, C, older embryos, in 

 longitudinal section. The archesporial cells are shaded. A, X4S0; B, C, X225. 



cells which there give rise to the meristem at the base of the 

 capsule. The form of the embryo is different too. It is pear- 

 shaped and more elongated than in Anthoceros. 



As the embryo develops these differences become more 

 apparent and others arise. Fig. 83, C shows a stage where 

 the division of the archesporial cells has begun, and it is at once 

 apparent how much more conspicuous they are. It is seen too 

 that the outer cells of the upper part of the capsule are also 

 dividing actively, and that, compared with Anthoceros^ the 



