250 . MOSSES AND FERNS CHAP. 



either be separate, or partly coherent, so as to form a single 

 crescent-shaped bundle, when seen in section. There may be, 

 however, even in this species, more than two strands present. 

 Poirault (2) found a definite endodermis in the lower part of 

 the stem, which disappears in the upper portion. 



Van Tieghem asserts (see Bower (16), p. 67) that in the 

 young sporophyte of O. vulgatum, there is at first a solid axial 

 stele, with pericycle and endodermis, and that only above the 

 insertion of the first leaf does a pith appear. 



In the bundles of the stem of O. pendulum, the xylem of the 

 collateral bundle is mainly composed of short irregular 

 tracheids, with close reticulate markings on the walls. The 

 phloem is composed of short, thin-walled cells with large nuclei. 

 No true sieve-tubes could be recognised. 



The Leaf 



The young leaf is completely concealed by the sheath formed 

 at the base of the next older one. It is at first a conical pro- 

 tuberance arising close to the stem apex, around which its base 

 gradually grows and forms the sheath about it and the next 

 leaf rudiment. It is probable that here, as in O. vulgatum* 

 the young leaf grows at first by a definite apical cell. After 

 the plant has reached a certain age, each leaf giyes rise to a 

 sporangial spike, which becomes evident while the leaf is still 

 very small. The first indication of this is a conical outgrowth 

 upon the inner surface of the leaf, about halfway between the 

 apex and base. A longitudinal section of this shows it to be 

 made up of large cells, especially toward the top ; but although 

 there was sometimes an appearance that indicated the presence 

 of a single apical cell, this was by no means certain, and if there 

 is such an initial cell, its divisions must be very irregular. 



Bower (16) found that in O. vulgatum the young spo- 

 rangial spike grows from a single apical cell, which in less robust 

 specimens persists for a long time as a four-sided, initial cell, 

 but in the larger specimens seems to be replaced by four similar 

 initials. 



The subsequent growth of the leaf is for a long time mainly 

 from the base, and the young sporangial spike is much nearer 

 the apex in the next stage (Fig. 133, B). No distinct petiole 

 ^ostowzew (i), p. 451. 



