544 



MOSSES AND FERNS 



CHAP. 



than in Marattia, the neck canal cell is shorter and extends but 

 little between the neck cells (Fig. 313, B). 



The egg is very large, round or oval in form, and the 

 nucleus contains a large nucleolus that stains very intensely, 

 but otherwise shows little chromatin. The receptive spot is of 

 unusual size, and occupies about one-third of the ^gg. It is 



Fig. 313. — Isoetes echinospora van Braunii. Development of the archegonium, X500; 

 o, the egg; v, ventral canal cell; h, neck canal cell; D, shows a two-celled embryo 

 within the archegonium. 



almost hyaline, showing, however, a faint reticulate arrange- 

 ment of fine granules ; the lower portion of the egg is filled with 

 granules that stain strongly. 



In /. lacustris, according to Hofmeister, only one arche- 

 gonium is formed at first, and if this is fertilised, no others are 

 produced ; but in /. echinospora, even before the first arche- 

 gonium is complete, two others begin to develop and reach ma- 

 turity shortly after the first, whether the latter is fertilised or 



