342 MOSSES AND FERNS CHAP. 



The central tetrahedral cell of the young sporangium (arche- 

 sporium) has cut off from it, by periclinal walls, the primary 

 tapetal cells (f), and in the meantime the wall of the capsule 

 forms repeated radial divisions but no periclinal ones, and, un- 

 like that of the eusporangiate Ferns, always remains single- 

 layered. A surface view of the sporangium at this stage shows 

 the last-formed lateral segment to still retain its triangular 

 form, and the cell divisions in it are very regular. After two 

 or three transverse divisions, a median vertical wall follows, 

 and in each of the resulting cells a transverse wall. Of the two 

 upper cells, one, according to Miiller, remains undivided, the 

 other divides again by a vertical wall, and the inner of the two 

 cells thus formed by further transverse divisions forms the 

 stomium or mouth of the sporangium. 



The cells of the young sporangium contain but little gran- 

 ular contents, and the divisions are very evident. As soon 

 as the archesporium is formed its contents begin to assume a 

 more granular appearance, and become more highly refractive 

 than those of the surrounding cells. The contrast between the 

 archesporial cells and those of the wall increases as the sporan- 

 gium grows older. 



The first division in the central cell begins soon after the 

 separation of the primary tapetal cells. The direction of this 

 first wall is usually transverse, but may be more or less inclined, 

 or even vertical. In each of these cells a wall is formed at 

 right angles to the first-formed, and the quadrant cells are 

 again divided into equal octants. Each of these eight cells 

 divides once more (Fig. 190, G), and the sixteen spore mother 

 cells, found in most Ferns, are complete. In Onoclea struthi- 

 opteris I found twelve as the ordinary number, but at what 

 point the division is suppressed was not made out. During the 

 division of the central cells the tapetal cells also divide, first by 

 radial walls only, but later by one set of periclinal walls. This 

 doubling of the tapetum, while it occurs in the majority of 

 Polypodiaceas, does not seem to be universal (Goebel (10), 

 p. 218). The cells of both sporogenous cells and tapetum have 

 dense granular cytoplasm, and large nuclei. Soon after the 

 divisions in the sporogenous complex are completed, the walls 

 of the tapetal cells become broken down, and their contents 

 dispersed through the large central cavity. The sporangium 

 continues to enlarge rapidly after this, and the spore mother 



