364 MOSSES AND FERNS CHAP. 



a spiral, but cases were sometimes encountered where the seg- 

 ments were apparently cut off in pairs from opposite sides of 

 the initial cell. The root-cap arises in part from special seg- 

 ments cut off from the outer face of the apical cell, but also in 

 part from the outer cells of the lateral segments, as in the Eu- 

 sporangiatse. The separation of the tissue system follows 

 much as in Botrychium. The central cylinder is large and oval 

 in section, but with poorly-defined limits, and it is not possible 

 to state positively whether it owes its origin exclusively to the 

 innermost cells of the segments. The large central tracheae, 

 as in Adiantum, are very early distinguishable. O. Claytoni- 

 ana agrees on the whole with O. cinnamomea, but the divisions 



A. 



FIG. 206. Osmunda regalis. A, Section of young sporophyll passing through three 

 very young sporangia; B, longitudinal section of an older sporangium; t, the 

 tapetum, X325 (after Bower). 



are much more regular, and it approaches nearer the typical 

 leptosporangiate type, both in the arrangement of the young 

 tissues and in the structure of the fully-developed vascular 

 bundle, which closely resembles that of the Polypodiacese, and 

 differs from the investigated species of Osmunda and Todect in 

 the better development of the endodermis, and in having the 

 pericycle of but one or two layers. The vascular cylinder of the 

 root is typically cliarch like that of the Polypodiaceae, but ex- 

 ceptionally (Faull (i), p. 22), it may be triarch. 



The roots arise regularly, two at the base of each leaf 

 (Lachmann (7), p. 118), and their bundles connect with those 

 of the stem near the bottom of the elongated foliar gap in its 

 vascular cylinder. 



