Z22 



MOSSES AND FERNS 



CHAP. 



embryo into the anterior epibasal half and the posterior hypo- 

 basal. The former produces the stem and cotyledon, the 

 latter the primary root and foot. The early divisions are 

 extremely regular, and offer a marked contrast to those in the 

 eusporangiate embryo. The second wall is the transverse 

 (quadrant) wall, separating the leaf and stem in the epibasal 

 part, and the root and foot in the hypobasal. The next walls 

 are the median or octant walls, but they do not correspond 



Fig. 178. — Onoclea sensibilis. A, two-celled embryo, X about 500; B, an eight-celled 

 embryo, longitudinal section; C, two longitudinal sections of an older embryo, X 

 about 250; D, E, two horizontal sections of a still older embryo; F, longitudinal 

 section of an advanced embryo; the cotyledon is beginning to project beyond the 

 other organs; cot, cotyledon; r, root; st, stem; /, foot. (All figures drawn from 

 sections made by Dr. W. R. Shaw.) 



exactly in all the quadrants. While in the cotyledon and stem 

 they are almost exactly median, in the root especially, the octant 

 wall diverges often a good deal from the median line, and the 

 two resulting octants are unequal in size. The following 

 divisions correspond for a short time in all the octants, but 

 soon show characteristic differences. For a short time each 

 octant shows a definite apical growth, the segments being cut 

 off by walls formed successively parallel to the three primary 



