SEXUAL REPRODUCTION. 



285 



387. The egg. — The egg is larger than the sperm, usually 

 non-motile and fixed. In aquatic algx the egg is sometimes 



Fig. 323. — Diagram of a longitudinal section of a pistil with one ovule, s, stigma, on 

 wiiich are lodged two pollen grains ; g, style ; (', ovularj' : y, ji, ai, it, together form 

 the ovule ; /, stalk ; !', megasporangium ; ai, outer integument ; //, inner integument ; 

 t\ megaspore. witli nucleus which is to develop later into \-egetati\e part of female 

 plant ; /', antipodal cells ; /.-, egg. and near by another ; 11/ , njicropyle ; /, pollen tube 

 entering it and reaching egg. — After Luerssen. 



free, escaping from the ovary in which it is produced, and 

 being fertilized by the sperms, which are likewise free in the 

 water, as in Fticus (fig. 324). Sometimes the egg itself is 

 ciliated and hence motile. In these cases it meets the motile 

 sperms in the water. 



The form of the egg is much less variable than that of the 



