OSMUND ACKAE 541 



and leaf, and even in the segmentation of the wings of the leaf, the condition 

 of Osmunda and Todea is less regular and more bulky than is habitual in 

 the Leptosporangiates : and in particular, in the segmentation of some of 

 their roots, where four prismatic initials take the place of the single initial of 

 the Leptosporangiates, there is a near approach to the structure seen in the 

 Marattiaceae : also in the apex of the leaf of Osmnnda and Todea there is 

 a three-sided initial cell, as against the usual two-sided type of the Lepto- 

 sporangiates. When these facts are put in relation with what has been 

 demonstrated for their sporangia, where there is so strange an oscillation 

 between the Eusporangiate segmentation and that typical of Leptosporangiate 

 Ferns, it becomes clear that the Osmundaceae hold a transitional place 

 as regards their embryonic, and meristematic structure. This harmonises 

 readily with their mature characters, and with their probable early origin as 

 shown by palaeophytological enquiry. 



Thus an examination of the Osmundaceae, living and fossil, leads to 

 the recognition of the following characters as probably existent in the stock 

 from which the family sprang. It had an upright, radially constructed shoot, 

 as shown both by the living species and by the related fossils ; for though the 

 embryo has the prone position in living forms, this is only a temporary juvenile 

 phase (see pp. 213-215). The axis was protostelic, as indicated by the 

 seedling structure, as well as by that of the earlier fossils : and though the 

 stele tended to be disintegrated in the more recent types there is still no 

 proof that the state of typical dictyostely was ever reached. The absence of 

 leaf-gaps in the early condition of the seedlings, and in the early fossils, as well 

 as the fact that the leaf-trace in all consists of a single strand, indicates an 

 ultimate origin from a stock in which the leaf had not attained the ascendant 

 in the shoot. The young parts were protected by mucilaginous hairs, 

 ramenta being absent. The disposition of the relatively bulky sporangia 

 was non-soral, either uniformly on both sides or margin of the leaf, or on 

 the lower surface : the individual spore-output was relatively large, and 

 the opening mechanism simple. These characters all point towards the 

 Botryopterideae among known early forms, and make it appear probable 

 that the source of the Osmundaceae is to be found in some near relation 

 to that early family of Ferns. 



