IX 



MA RA Tl -I A CEAL—ISOE TA CE/E 



285 



a depression is evident, which separates the bases of the 

 cotyledon and root. The base of the latter, which begins 

 now also to grow in length, projects in the form of a semi- 

 circular ridge that grows rapidly and forms a sheath about the 

 ligule and the base of the cotyledon (Fig. 152, v). The growth 

 of this sheath is marginal, and continues until a deep cleft is 

 formed. A number of cells at the bottom of the latter between 

 the sheath and the leaf base constitute the stem apex. As 



Fig. 149. — A, An embryo of /. echinospera var. Braunii, with unusuallj- regular divisions, X4;o; 

 B, a much older one, still enclosed within the prothallium, X 150 ; ar, archegonia. 



they differ in appearance in no wise from the neighbouring 

 cells, it is quite impossible 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.^ 



Longitudinal sections of the embryo, when root and leaf 



are first clearly recognisable, show that the foot is not clearly 



defined, as the basal wall early becomes indistinguishable from 



the displacement due to rapid cell division in the axis of the 



^ See Hanstein's figures of Alisma, for example, in Goebel's Outlines, Fig. 332. 



