I04 



MOSSES AND FERNS 



CHAP. 



archesporium. Both longitudinal and transverse sections of 

 the sporogonium at this stage (Fig. 47) show a good deal of 

 irregularity in the arrangement of the cells, and the first 

 periclinal walls form at very different distances from the 

 surface, so that it is clear that the wall cannot be established, 

 as in Radula for instance, by the first periclinals. 



The cells of the older archesporium are arranged in more or 

 less evident rows radiating from the base (Fig. 48, A). No 

 definite relation of spores and elaters can be made out, the two 

 sorts of cells being mingled apparently without any regular order. 

 Some of the cells cease dividing and grovv^ regularly in all direc- 



FiG. 47. — Porella Bolanderi (Aust.). Development of the embryo. A-D, in longitudinal section ; 

 E-G, transverse sections. B and C are sections of the same embryo, and E, F, G are 

 successive sections of a single embryo, X525. 



tions, while others may divide further and grow mainly in the 

 plane of division, so that they become elongated. The former 

 are the young spore mother cells, the latter the elaters (Fig. 48, 

 C). The division of the spores begins while the cells of the 

 archesporium are still united, although at this time the swollen 

 and strongly striated cell walls of the mother cells (Fig. 48, C) 

 show that they are becoming mucilaginous. At this stage 

 sections through the archesporium show the deeply -lobed 

 spore mother cells with the elongated elaters packed in between 

 them, the pointed ends of the latter fitting into the interstices 

 between the spore mother cells. The latter are somewhat 

 angular and the wall distinctly striated. It is the inner layer 



