4o8 



MOSSES AND FERNS 



CHAP. 



traversine the centre is concentric, with a definite endodermis, 

 but the tracheary tissue is very slightly developed. This 

 becomes first visible about the time the leaf breaks through the 

 calyptra. 



The Stem 



Of the two octants in the stem quadrant one becomes at 

 once the apical cell of the stem, the other the second leaf, 

 as in other Leptosporangiatae. The first wall in each octant 

 meets octant and quadrant walls, and cuts off a large cell 



Fig. 213.— Longitudinal section of the young sporophyte of Pilularia glohilifcra, still enclosed in 

 the calyptra {cat), and attached to the macrospore {sp), x 75 ; B, the lower part of the same 

 embryo, X215 ; r, apical cell of the root ; st, apical cell of the stem; /, lacuna;. 



from each octant, in contact with the foot. Hanstein and 

 Arcangeli regard these as part of the foot, and physiologically 

 they no doubt are to be so considered, but morphologically they 

 are beyond question segments respectively of the stem and second 

 leaf. At first these are not distinguishable from each other, but 

 the divisions in the latter are usually (in Pilularia) less regular, 

 and the apical cell early lost. It may, however, develop a 

 regular three -sided apical cell, like that of the later leaves. 

 The earlier segments of the stem apex are larger than the 

 subsequent ones, and the broadly tetrahedral form of the 



