XII 



LEPTOSPORANGIA Ty£ HETEROSPOREJL 



387 



nuclei and divide for a time after the manner of two-sided 

 apical cells, and perhaps the first division of the leaf quadrant 

 may be of the nature of a true dichotomy, and these cells are 

 the apical cells of the two lobes. \n the four-sided cell, the 

 radial and tanrential divisions succeed each other with much 



Fk;. 199. — Azolia/iliculoidcs {'La.m.). Development of the embr>'0, X350. A, B, C, Young embryos 

 in median longitudinal section ; D, two horizontal sections of a young embrj-o ; E, three 

 transverse sections of a somewhat older one ; x, -V , initial cells of the cotyledon ; F, two longi- 

 tudinal sections of an advanced embryo ; G, horizontal section of an older one, with the rudiments 

 of the second and third leaves ; b, b, basal wall of the embryo ; st, stem ; L 1, cotyledon ; r, root ; 

 k, hairs ; x, apical cell of the stem ; L'-, L3, second and third leaves. 



regularity. By the growth of the two initials (Fig. 199, E, 

 X, x') the young cotyledon rapidly grows at its lateral margins 

 and bends forward so as to enclose the stem apex. At the 

 same time the upper marginal cells divide rapidly by oblique 



