262 



MOSSES AND FERNS 



CHAP. 



nucleus of the sperm cell previous to the differentiation of the 

 spermatozoid. The two nuclei then gradually fuse, but all the 

 different stages could not be traced. Before the first division 

 takes place, however, but one nucleus can be seen, and this 

 much resembles the nucleus of the unfertilised &gg. 



After fertilisation the Qgg enlarges to several times its 

 original size before dividing. The first (basal) wall is transverse 

 and is followed in each half by two others, the median and 

 octant walls. The nearly globular embryo is thus divided into 



Fig. 135. — Marattia Do7iglasii (Jjsker). Embryogeny. A, Longitudinal ; B, transverse sections of 

 embrj'os, X215 ; C, vertical section of an older embryo, shovi'ing its position in the prothallium, 

 X 72 ; st, the stem ; pr, prothallium ; D, upper part of the same embryo, X 215. 



eight similar cells, each having the tetrahedral form of a globe 

 octant. The next divisions are not perfectly understood, and 

 evidently are not absolutely uniform in all cases. All the 

 octants at first show nearly uniform growth, and the embryo 

 retains its nearly oval form (Figs. 134, F, 135, A). The first 

 division in the octants is essentially the same, and consists in a 

 series of anticlinal walls, before any periclinal walls appear, so 

 that we may say that for a short time each octant has a dis- 

 tinct apical growth, and there are eight growing points. The 



