144 



3I0SSES AND FERNS 



CHAP. 



a mass of archesporial tissue much thicker than that below, 

 and occupying very much more space than the corresponding 

 tissue in Anthoceros. Longitudinal sections through the basal 

 part of the older sporogonium show an arrangement of tissues 

 similar to those in Anthoceros, but there are differences corre- 

 sponding to those in the young stages. The foot (Fig. 72, A) 

 is much smaller and flatter, and sometimes shows a very regular 

 structure. The central part is composed of a compact mass of 

 rather large cells, between which and the base of the capsule is a 

 narrow zone of meristematic tissue. The superficial cells do not 

 always grow out into the root-like processes found in Anthoceros 



B 



Fig. 71. — Notothy las orbicularis {SuW.). A, Four-celled embryo ; B, C, older embryos, in longitudinal 

 section. The archesporial cells are shaded. A, X450; B, C, X225. 



and Dejidroceros, but may remain short and project but slightly. 

 The cells are characterised by abundant granular cytoplasm and 

 conspicuous nuclei, showing that they are probably not only 

 absorbent cells, but also elaborate the food materials taken in 

 from the gametophyte. The gradual transition of the differen- 

 tiated tissues above into the meristem at the base, is precisely 

 as in Anthoceros, and sections at that point in the two genera 

 can scarcely be distinguished from one another. The columella 

 (in longitudinal section) in both shows four parallel rows of 

 cells, outside of which lies the single row of archesporial cells, 

 and four rows of cells belonging to the wall of the capsule. 



As the section is examined higher up, however, there are 



