XI THE HOMOSPOROUS LEPTOSPORANGIAT^ 353 



through which the leaf-traces pass from the axial bundles to 

 the leaves. Each leaf-trace is surrounded by a sheath of 

 colourless cells. 



The origin of the leaves is the same as in the Polypodiaceae, 

 but the young" leaf grows from a three-sided apical cell much 

 like the stem/ and the young leaf is more conical than there. 

 In the very young leaf, according to Bower, one side of the 

 apical cell is always directed toward the stem apex, and never 

 one of the angles. In the presence of a three -sided apical 

 cell, as well as its more cylindrical form, there is an approach 

 to BotrycJiiuni. The further development of the leaf is like 

 that of the pinnate leaves of the Marattiacea; or Polypodiaceae, 

 with which they agree also in the strongly circinate vernation. 

 The leaves are always pinnately divided, and are similar in all 

 the forms, and the type of venation is the same. While in all 

 species of Osnmnda and in Todea barbara, the structure of the 

 leaf is quite like that of the Polypodiacese, the other species of 

 Todea i^Leptopteris) have the lamina of the leaf reduced to two 

 or three layers of cells, and there are no stomata. The 

 texture of the leaves in these forms is filmy, like that of 

 Hymenophyllu ni . 



The petiole is traversed by a single large vascular bundle, 

 which in section is crescent-shaped and in structure concentric, 

 with the elements like those of the Polypodiacea;, but the 

 endodermis is not so clearly differentiated, and close to the 

 inner side of the bundle are numerous mucilage cells, recalling 

 the tannin ducts of Angiopteris. A further point of resem- 

 blance to the Marattiaceai is the presence of stipular wings at 

 the base of the petiole. The chaffy scales (palese) so common 

 in the Polypodiaceae are quite wanting, but hairs are developed, 

 often in great numbers. Thus in O. cinnamoinea the young 

 leaves are covered completely with a felted mass of hairs, 

 recalling those in some of the Cyatheaceae. Some of these are 

 glandular. The sterile leaves and sporophylls are either very 

 much alike, as in Todea, or the sporophylls may be very 

 different. An extreme case is seen in O. cinnamoinea, where 

 the whole sporophyll is devoted to the development of 

 sporangia. In this species, as well as O. Claytoniana, the 

 sporophylls develop first and form a group in the centre of a 

 circle of sterile leaves. In O. cinnainoniea the sporophylls 



' Bower (11), p. 332 ; Klein (2), p. 647. 

 2 A 



