ii8 



MORPHOLOGY 



Sporophyte. — The sporophyte is the most characteristic and com- 

 plicated structure in true mosses (fig. 254). As it develops from the 

 fertilized egg, the venter and stalk of the archegonium 

 develop a remarkable calyptra, which enlarges very 

 much, but is finally ruptured near the base by the 

 growing sporophyte and is carried up as a cap or hood 

 on the top of the capsule. The first division of the 

 egg is transverse, and an apical cell with two cutting 

 faces is developed in the outer cell or in some one of 

 its early progeny. A variable number of segments 

 is cut off (fig. 258), resulting usually in a much 

 elongated embryo. In the upper end of the embryo 

 the usual differentiation into amphithecium and endo- 

 thecium occurs ; the former develops into several 

 layers, the latter into quite a mass of cells (figs. 259, 

 260). The sporogenous tissue is cut off late from the 

 periphery of the endothecium, but does not cap the 

 columella, which extends completely through the 

 capsule as an axis (figs. 261, 262). The sporogenous 

 tissue becomes two layers of cells, the mass not being 

 dome-shaped, as in Anthoceros 

 and Sphagnum, but barrel-shaped. 

 Among bryophytes, the sporoge- 

 nous tissue, therefore, reaches its 

 greatest relative reduction in true 

 mosses. 



Fig. 258. — True 

 moss: ayoungsporo- 



FlG. 257. — True Capsule. — The final structure of the 



moss: an archego- capsule is extremely complex, and a 



nium, showing the longitudinal section may be outlined as 



conspicuous stalk, foUo^g (fig, 263), beginning with the out- 



^. ., . side: (i) the epidermal layer, (2) several 



the axial row (com- ^ ' *^ . , . 



posed of egg, ventral '^>'^''^ °^ "'^". '^'="=' (3) a region of inter- 



canal cell and nu- cellular cavities traversed by threads of 



merous disorganized chlorophyll tissue, (4) a tapetal layer phyte,'*sliowrng''"the 



neck canal cells). (see p. 126) ; these four regions belong to ^o^k'of the apical 



the amphithecium. The endothecium is cell. After Barnes 



differentiated as follows : (5) the two layers of sporogenous and Land, ined. 

 cells, (6) an inner tapetal layer, (7) a region of intercellular 

 cavities traversed by threads of chlorophyll tissue, (8) the columella. The 

 inner region of cavities (7) is present only in such peculiarly organized forms 

 as Polytrichum. At the maturity of the capsule the water fails, all the 



