356 



MOSSES AND FERNS 



CHAP. 



tracts until it becomes oblong, and in close contact with the egg 

 nucleus, in some cases looking as if it had penetrated the egg 

 nucleus as it does in Onoclea (Shaw (2)). The process is a 

 slow one, and in one case twenty- four hours after the entrance 

 of the spermatozoid the two nuclei were still recognisable. 

 Finally they are completely fused, and a single nucleus, with 

 usually, perhaps always, two nucleoli is seen. No sign of a 

 separation of the chromosomes of the copulating nuclei was 

 observed. 



The Embryo 



The first division of the ovum is the same with respect to 

 the archegonium as in Onoclea, i. e., the basal wall is parallel 



Fig. 198. — A, Vertical section of an eight-celled embryo of O. Claytoniana, X260. 

 Median longitudinal section of an older embryo of the same species, X260; C, 

 two transverse sections of a somewhat younger embryo of O. cinnamomea, X260; 

 St, stem apex; L, cotyledon; r, primary root; F, foot. 



with its axis; but the quadrant wall is also parallel with this 

 instead of transverse, although its position with reference to the 

 axis of the prothallium is the same; so that the embryo-quad- 

 rants, and the organs derived from them, are situated like those 

 of the polypodiaceous embryo, with reference to the prothal- 

 lium, but not to the archegonium. 



