Cavers: Notes on Yorkshire Bryophytes. 453 



The archegonia are developed in groups, of which there may 

 be several on the same plant, standing- on the dorsal surface of 

 the midrib. Each group contains several (10-20) archegonia, 

 and is at first surrounded by a number of narrow, scale-like 

 outgrowths from the surface of the midrib, together with 

 mucilage-hairs. The scales become later joined at the base 

 and grow together, forming a short toothed sheath (involucre) 

 around the group. The archegonia standing nearest the apex 

 of the thallus are the youngest in the group, and a fairly com- 

 plete series of stages in the development of these organs may be 

 observed in a single group. After a time there appears, within 

 the toothed involucre, a ring of tissue which grows up and 

 gives rise to an inner sheath (perianth), the margin of which is 

 entire or slightly lobed. Should none of the archegonia in 

 the group be fertilised, the perianth remains very short, but 

 immediately fertilisation occurs the growth of the perianth is 

 resumed and it soon becomes much longer than the involucre, 

 which remains as a fringe round its base (Plate, II.). 



A longitudinal section through a half-ripe sporogonium shows 

 a well-marked division into capsule, seta, and foot (Fig. 5, I.). 

 The foot is conical and penetrates the tissue of the midrib ; the 

 seta consists of longitudinal rows of short cells. In the capsule 

 the wall is seen to consist of 4-6 (mostly 5) layers of cells, the 

 outer layer being nearly as thick as the inner layers taken together 

 and consisting of large cells, roughly cubical in form (Fig. 5, II.). 

 The elaters and spore-forming cells show a fairly regular arrange- 

 ment in alternating longitudinal rows. A similar section through 

 a ripe sporogonium still enclosed in the calyptra shows that the 

 short and broad cells of the seta are packed with small starch- 

 grains. The cells forming the outer layer of the capsule-wall 

 (Fig. 5, III.) now have their lateral walls thickened and coloured 

 deep brown, whilst the cells of the inner layers have lost their 

 protoplasm and become flattened and disorganised, so that the 

 capsule-wall consists practically of a single layer of large oblong 

 cells. The outer and inner tangential walls of these cells remain 

 thin, but the radial walls are greatly thickened and of a deep 

 brown colour. Towards both the base and the apex of the cap- 

 sule, however, some of the inner cells of the capsule-wall persist, 

 and in these regions we find on the inner surface of the large- 

 celled layer a number of narrow cells, the walls of which often 

 bear irregularly ring-shaped brown thickening-bands. 



The capsule eventually bursts through the calyptra and is, 

 carried up to a height of 30 mm. or more by the elongation of 



1903 December i. 



