ZYGOPTERIS 321 



towards the base of the sporangium. But on the 

 other two sides (alternating with the former) the cells 

 are larger, with thicker walls, and with their maximum 

 dimension vertical to the surface of the capsule (see 

 Fig. 1 1 9). These larger cells thus form a vertical 

 annulus, but one of a very peculiar kind, for it consists 

 not of a single row of cells, but of a broad band, many- 

 cells in width (see Fig. 119, 2 and 3). At the summit 

 of the sporangium the cells of the annulus thin out some- 

 what, so that we may regard it, if we like, as double, 

 consisting of two distinct bands, one on each side. 

 The pedicel is traversed, up to the base of the capsule, 

 by a concentric vascular bundle, a condition very rare 

 among recent Ferns, though approached in Helmintho- 

 stachys and Botrychium. The pedicel, however, is best 

 regarded as a branch of the rachis rather than as a 

 sporangium-stalk. 



Numerous spores are contained in the sporangia ; 

 they measure .08 mm. in diameter, which would be 

 an ordinary size for the spores of recent Ferns. They 

 are of the tetrahedral type, as is shown by the presence 

 of the three radiating ridges, which are often visible on 

 theexospore. M. Renault found other spores, of similar 

 dimensions, in the same sporangia, which do not show 

 the triradiate marking, but present a -reticulate appear- 

 ance, suggesting the presence of a group of polygonal 

 cells within their cavity. This appearance has proved 

 to be illusory, and the difference in the spores no doubt 

 depends simply on their condition at the time of 

 preservation, and is no indication of heterospory. The 

 type of fructification is rather that of a homosporous 

 member of the Filicineae. The leaves, or divisions of the 



