454 



MOSSES AND FERNS 



CHAP. 



the nucleus is decidedly larger than before fertilisation. The 

 lower neck cells approach and apparently become grown to- 

 gether, and as the divisions in the lower neck cells here contrib- 

 ute to the calyptra, the young embryo becomes more deeply 

 sunken in the prothallial tissue than is common in the Ferns. 

 The basal wall is transverse, as in the Marattiacese, and the 

 formation of the quadrants takes place as usual. The position 

 of the quadrant walls is, however, sometimes slightly different, 



Fig. 264. — ^A, Longitudinal section of the venter of a recently fertilised arclieg'onitlin, 

 X300; B, a similar section of an arcliegonium with the young embryo; C, D, two 

 transverse sections of a somewhat older embryo, X300; st, apical cell of the stem; 

 r, apical cell of the root; E, longitudinal section of an older embryo, X300; I, I, 

 the basal wall. 



being often decidedly inclined in both epibasal and hypobasal 

 halves (Fig. 264, E). In the former the larger of the two 

 primary cells is the initial for the stem, and its large size, com- 

 pared to the leaf quadrant, already points to the greater develop- 

 ment of the stem in the sporophyte compared to the leaves. Of 

 the hypobasal quadrants the larger becomes at once the root, 

 whose axis is nearly coincident with that of the stem. 



Jeffrey ( (2), p. 169) thinks that in E. hiemale the root also 

 may be of epibasal origin, but his figures 7 and 8 are capable of 



