SPOROGONIUM OF MNIUM. 351 



three to five in number, stand in front of the teeth of the outer 

 peristome. 



A delicate cross-section, taken somewhat deeper through the 

 capsule, shows in the centre of this a column formed of large- 

 celled tissue, the columella. Around this columella lies the 

 cavity filled with spores. The inner wall of this is formed by the 

 columella itself, the outer by a layer of tissue, usually two cells 

 thick, and containing chlorophyll, which appears separated from 

 the wall of the spore-capsule by a very loose chlorophyll-con- 

 taining tissue. The wall of the capsule consists of two or three 

 layers, and is covered by a sharply-defined epidermis. The cells 

 of this latter are more strongly thickened on their outer walls. 

 The spores contain chlorophyll grains, their wall is brownish, 

 and studded ( with tiny warts ; in favourable cases a three-sided 

 pyramidal tapering of one side of the spore can be noticed, which 

 arises from the tetrahedral position of the quartette of spores 

 inside their mother-cell ; it indicates the contact surfaces of its 

 three sister- spores. 



A perfectly median longitudinal section, which we prepare 

 from a capsule which is still green and provided w r ith its oper- 

 culum, but is already fully formed, shows us uppermost the lid, 

 consisting externally of one sheath of browner, strongly-thickened 

 cells, and internally of many layers of thin-walled cells. At the 

 limits between lid and urn lies the double layer of the obliquely 

 arranged, chlorophyll-containing cells, already known to us, by 

 which the separation of the lid is effected. The adjoining brown 

 cells of the urn below are distinguished by then' small height. 

 Similar cells adjoin these small ones towards the interior, and 

 form thus an inward projecting ledge of thickened, brown cells, 

 on which are set the teeth of the outer peristome. About the 

 thickness of a cell removed arise the cilia. As the history of 

 their development teaches us, these teeth and cilia arise by local 

 thickening of the opposite walls of one and the same layer of cells 

 adjoining the inside of the lid. The teeth proceed from definite 

 portions of the outer walls, connected in the ascending direction ; 

 then- cross-ridges indicate inner adjoining cross-walls, upon which 

 the thickening has continued for some little distance. The cilia 

 proceed from the thickened parts of the inner walls of this same 

 layer of cells, and bear slight ridges at the places of junction 

 of the next inner partition walls. In our median longitudinal 

 section the lid is hollow ; the inner tissue, after the formation 



