LEPTOSPORANGIAT^ HETEROSPORE^ 



427 



usually continue long, and the subsequent growth is purely 

 basal. The cotyledon is alike in both genera, and is a slender 

 cylindrical leaf tapering to a fine point, where the cells are much 

 elongated and almost colourless. Its growth is at first slow, 

 but at a later period (in Pihilaria globulifera about the eighth 

 day) it begins to grow with great rapidity and soon reaches its 

 full size. This is largely due to a simple elongation and ex- 

 pansion of the cells, which are separated in places, and form a 

 series of longitudinal air-channels separated by radiating plates 

 of tissue (Fig. 251, i). The simple vascular bundle traversing 



Fig. 251. — Longitudinal section of the young sporophyte of Pilularia globulifera, still 

 enclosed in the calyptra {cat), and attached to the macrospore {sp), X75; B, the 

 lower part of the same embryo, X21S; r, apical cell of the root; st, apical cell of 

 the stem; i, lacunae. 



the axis 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 from each 



