1 86 



SECOND GROUP. MUSCINEAE. 



A 



capsule, or an annular layer of epidermal cells, the annulus, is thrown off by the 

 swelling of its inner walls and the lid is thus separated from the capsule. The margin 

 of the capsule in the majority of species is seen after the removal of the operculum 

 to be occupied by one or two rows of appendages of very regular and delicate 

 structure; the single appendages are known as teeth and cilia, and together they 

 constitute the peristome ; where there is no peristome the capsule is said to be gym- 

 nostomous. The capsule is at first a solid mass of homogeneous tissue ; the 

 differentiation of its interior begins with the formation of an intercellular space of 

 annular form, which now separates the wall of the capsule composed of several layers 



of cells from the central tissue, but the tissue of the wall 

 continues to be connected with the tissue of the base and 

 apex of the columella ; the intercellular space is traversed 

 by rows of cells stretching from the wall to the inner 

 tissue, which are very like protonemal or algal filaments, 

 but are merely a product of the differentiation of the tissue 

 of the capsule, and, like the inner cell-layers of the wall, 

 contain chlorophyll-corpuscles. The outer layer of the 

 wall constitutes a highly characteristic and strongly 

 cuticularised epidermis. The third or fourth layer of 

 cells of the inner tissue, which is separated therefore 

 from the annular air-cavity by two or three cell-layers 

 forming the spore-sac, is the archesporium ; its cells are 

 at first densely filled with protoplasm in which is a large 

 central nucleus, and are united with the surrounding 

 tissue without interstices like cells in a parenchyma. 

 The spore-mother-cells are the product of the division of 

 the cells of the archesporium, which now separate from 

 one another by the deliquescence of their cell-walls and 

 float free in the fluid which fills the interior of the 

 spore-sac, till by further division they produce the spores. 

 The term outer spore-sac is applied to the layers of cells 

 which divide the large air-cavity from the spore-mother- 

 cells, while the layers which bound them on the side next 

 the axis (Fig. 147, z) form the inner spore-sac ; the cells 

 of both contain chlorophyll-corpuscles which form starch. 

 The inner large-celled tissue without chlorophyll, which 

 is thus surrounded by the spore-sac, is the columella. 

 The spore-sac is ruptured by the removal of the oper- 

 culum, the columella dries up, and in the Polytrichaceae 

 there remains a layer of cells spreading horizontally over 

 the space covered by the operculum ; this layer, which is 

 attached to the points of the teeth and stretched upon 

 them over the mouth of the capsule, is the epiphragm. 



The origin of the peristome requires to be examined somewhat more in detail. In 

 genera which, like Gymnostomum, have no peristome, the parenchyma which fills the 

 inside of the operculum is homogeneous and thin-walled ; when the capsule is mature it 

 dries up and shrinks into the bottom of the operculum which essentially is formed only 

 of the epidermis, or it remains attached as a thickening to the summit of the columella 

 and projects above the mouth of the capsule, or it forms a diaphragm covering the mouth 

 of the capsule after the lid has fallen away, as in Hymenostomum. Tetraphis forms' a 

 transition to the genera which have true peristomes ; in Tetraphis the firm epidermis of 

 the upper conical portion of the capsule falls off as an operculum, while the tissue 

 contained in it, the two outer layers of which are thick-walled, splits cross-wise into four 

 lobes, which are called by systematists a peristome, though their origin and structure are 



FlG. 144. Funaria hygrometrica. 

 Transverse section through the spore- 

 sac ; snt in A the archesporium, sm in B 

 the mother-cells of the spores not yet 

 isolated, a outer, * inner side of the 

 spore-sac ; magn. 500 times. 



