264 



MORPHOLOGY 



kind, but the megaspores are represented by four nuclei. The mother 

 cell, therefore, seems to behave like a megaspore in producing the female 

 gametophyte, and the hypodermal initial thus directly produces the 

 female gametophyte. Of course this really means that four mega- 

 spores enter into the formation of the gametophyte, and the two 

 successive reduction divisions are the first two divisions in the forma- 

 tion of the gametophyte. 



Female Gametophyte 



Development. — The development of the female gametophyte of 

 angiosperms begins with free nuclear division, as in gymnosperms, but 

 the nuclei thus produced are definitely eight in number, following three 

 successive divisions from the nucleus of the megaspore. It is in this 

 free nuclear stage that the egg is differentiated, which is the condition of 

 Gnetum, except that here the nuclei are much fewer in number. In 



Figs. 589-591. — Development - of female gametophyte of angiosperms, as shown by a 

 lily: 589, megaspore (in the ovule); 590, first division; 591, second division. 



connection with these free nuclear divisions two remarkable features 

 appear. One is the polarity exhibited by the nuclei. After the first 

 division the two nuclei separate and pass to the poles of the embryo sac, 

 one to the micropylar end; and the other to the antipodal end (fig. SQo). 

 There follow two successive divisions, so that first two (fig. 591) and then 

 four (fig. 592) nuclei are produced at each pole of the sac. The other 



