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PLANT LIFE. 



Heterogamy. 



Heterogamy is that mode of sexual union in which the sex 

 cells are unlike, being differentiated into sperms and eggs. 



380. The sperms. — The body of the sperm is the cell 

 nucleus, surrounded by a small amount of protoplasm which is 

 often extended into one or more cilia (fig. 306). The more 

 complete the differentiation of the sperm the smaller, as a 

 rule, is the amount of body protoplasm. Whether or not* the 

 sperm is motile depends upon the conditions to which it has 

 become adapted. Whenever motile, fertilization must occur 

 in the presence of water of amount sufficient to permit the 

 sperm to swim to the egg. 



Fig. 306. — Sperms of various plants, showing variety of form, i, Volvox aureus; 

 2, Vaucheria synandra ; 3, Ckara fragilis ; 4, Fucus serratus ; 5, Marchantia 

 polymorpha ; 6, Equisetum Telmateia : 7, Marsilia z>estita. Magnified 1000 

 diam.— After Mobius. 



The spermary may produce only one sperm (fig. 307), or 

 its contents may divide into many (fig. 310). When single, 



