X FILICINE.-E LEPTOSPORANGIATjE 319 



somewhat different, and the first wall is a radial one, instead of 

 pericHnal. The stem is very short at the time the young 

 sporophyte breaks through the prothaUium, and its apex more 

 pointed than is afterwards the case. 



TJie Root 



At first the segmentation of the apical cell of the root is 

 almost exactly like that of the stem, and it is not until several 

 lateral segments, usually about two series of them, have been 

 formed that the first periclinal wall, cutting off the first cell of 

 the root-cap, is formed. There is a good deal of difference, 

 however, as to the time this occurs, and there is probably some 

 connection between it and the different period at which the 

 primary root breaks through the calyptra. In most Poly- 

 podiaceae the root is the first of the organs to penetrate the 

 calyptra, but sometimes in Onoclea it is still short at the time 

 the cotyledon is nearly developed, and in this recalls Marattia, 

 where this is regularly the case. As soon as the first segment 

 of the root -cap is formed, the segmentation of the root is 

 extremely regular, and corresponds essentially to that found in 

 the later roots. 



The Foot 



All definite divisions cease very soon in both of the foot 

 octants, and this part of the embryo forms a more or less 

 projecting hemispherical mass of cells, closely appressed to the 

 prothallial cells. As usual in such cases the outer cells are 

 large and distinct. 



Shortly before the embryo breaks through the calyptra, 

 which takes place much earlier than in Marattia, the first traces 

 of the vascular bundles are seen as strands of procambium cells 

 occupying the axis of each of the primary organs, and united in 

 the centre, so that the four bundles together form a cross. Of 

 these the one going to the foot is short, and ends blindly within 

 that organ, but the others continue to grow with the elongation 

 of the members to which they belong. The first permanent 

 tissue to be recognised forms, as in Ularattia, a bundle of short 

 irregular tracheids at the junction of the young bundles 

 (Fig. 161, D). These primar}^ tracheids in Onoclea are 

 scalariform, but the pits are shorter than in the later ones. 



