187 



majority of the Liverworts some of these cells are sterile and 

 become elaters (cells with spirally thickened walls, Figs. 196, 189), 

 or serve as " nurse-cells " for the spore-mother-cells, which gradu- 

 ally absorb the nutriment which has been accumulated in them. 

 In Anthoceros, and almost all the Leafy-Mosses, a certain mass of 

 cells in the centre of the sporangium (derived from the endo- 

 thecium) does not take 

 part in the formation 

 of the archesporium, 

 but forms the so called 

 "column" or " colum- 

 ella" (Figs. 190, 191). 

 The spores arise in 

 tetrads, i.e. four in each 

 mother-cell, and are 

 arranged at the corners 

 of a tetrahedron, each 

 tetrahedron assuming 

 the form of a sphere or 

 a triangular pyramid. 

 The mature spore is a 

 nucleated mass of pro- 

 toplasm, with starch or 

 oil as reserve material. 

 The wall is divided into 

 two layers: the exter- 

 nal coat (exospore) 

 which is cuticularized 

 and in most cases 

 coloured (brown, yel- 

 lowish), and the internal 

 coat (endospore) , which 

 is colourless and not 

 cuticularized. On ger- 

 mination the exospore 

 is thrown off, the endo- 

 spore protrudes, and 

 cell-division commences 

 and continues with the growth of the protonema (Fig. 186, B-D).. 



The morphological explanation which Celakovsky has given of the sporo- 

 gonium, and which is not at all improbable, is, that it is homologous with* 



FIG. 193. Andrecea petro- 

 pMla. An empty capsule ; 

 the calyptrahas fallen off. 



(Mag. 25 times.) 

 / 



FIG. 192. Andrecea petrophila. A ripe sporogonium : 

 a an archegonium which has been raised with the 

 pseudopodium ; p the foot ; 6 the neck ; d-e the dark- 

 coloured portion of the sporangium, whose outer cell- 

 walls are considerably thickened ; c-c the thin-walled 

 portions where the dehiscence occurs ; o the lower ex- 

 tremity of the spore-sac; /calyptra; g the apex of 

 the sporangium. (Mag. 25 times.) 



