MOSSES AND FERNS 



CHAP. 



grow -in length, projects in the form of a semi-circular ridge that 

 grows rapidly and forms a sheath ahout the ligule and the base 

 of the cotyledon (Fig. 317, v). The growth of this sheath is 

 marginal, and continues until a deep cleft is formed. A num- 

 ber of cells at the bottom of the latter between the sheath and the 

 leaf base constitute the stem apex. As they differ in appear- 

 ance in no wise from the neighbouring cells, it is quite impossible 



FIG. 316. Three successive horizontal sections of a somewhat advanced embryo of 

 /, echinospora var. Braunii, X26o; R, root; cot, cotyledon; st, stem; I, ligula. 



to say just how many of them properly belong to the stem. So 

 far as can be judged, the origin of the growing point of the 

 stem is strictly secondary, and almost exactly like that of many 

 Monocotyledons. 1 



Longitudinal sections of the embryo, when root and leaf are 



1 See Hanstein's figures of Alisma, for example, in Goebel's Outlines, 

 Fig. 332. 



