ATRICHUM UNDULATUM. lot 



The tissues of the seta attain rather higher devel- 

 opment than those of the stem. The cortical part is 

 provided with a well formed epidermis, while the axial 

 part is composed of several tissues, the two portions 

 being separated by thin-walled parenchyma. At the 

 apophysis, where the seta expands at its upper end, 

 many mosses produce stomata quite like those of 

 higher plants. In rarer instances they occur on the 

 capsule or seta. Their presence or absence seems to 

 signify nothing as to relationship, as there is no more 

 constancy in their occurrence among the highest than 

 among the lowest forms." 



The capsule of Atrichum does not differ widely from 

 that of other mosses, except in the teeth and epi- 

 phragm, and otherwise requires no particular explana- 

 tion. The teeth are composed of groups of cells 

 arranged as a series of U's placed side by side. In all 

 other mosses except the immediate allies, where teeth 

 are present at all, they are formed of the thickened 

 sides of the cells, and not of whole cells. 10 The epi- 

 phragm, which joins the apices of the teeth like a thirf 

 membrane, is formed without thickening or special 

 preparation of the walls. The spores escape by being 

 shaken from the capsule through the openings between 

 the teeth, as from a pepper box. 



The calyptra, which is the result of the aftergrowth 

 of the archegonium, was early torn away from its 

 attachment at the base of the fruit and carried up by 

 the elongating seta as a hood for the capsule. 



9 Valentine, Trans. Linn. Soc. , xviii, p. 239. 



10 Sachs, Text-book, 2nd Eng ed., p. 383. 



