228 



REPRODUCTION 



em 



Fig. 131. — Stages in the formation of the megaspore, its germination, fertilization of 

 the egg and. endosperm nuclei, and germination of fertilized egg and endosperm cells. -4, 

 beginning of ovule at 0; B, nu, nucellus; Ca, nu, nucellus, a, archesporium; in, forward 

 growth of tissue to form the integument; Cb, nu, nucellus; in, integument; D, more highly 

 magnified drawing of o in A showing archesporial cell at a; E, a, archesporial cell enlarged 

 and ready for division ; M«, tissue of the nucellus ; F, a, archesporial cell dividing, «», nucellus; 

 G, row of four megaspores descended from the archesporial cell, only the upper one, m, 

 functional, the others soon to disintegrate; H, the megaspore, m, enlarging, the pthers 

 disappearing; /, nucleus of the megaspore divided into two, md; J, continued nuclear 

 division has resulted in eight, namely, three antipodal nuclei, an, at the upper end of the 



