CHAPTER VII 

 FERTILIZATION 



It is easy to write a chapter heading ''Fertilization." 

 but it is not so easy to determine just what should be 

 included in that chapter. Some writers would define 

 fertilization as the union of definitely organized male 

 and female elements; but in many of the lower plants, 

 where the essential features are the same as in the flower- 

 ing plants, the two gametes, as the two uniting elements 

 are called, are certainly not definitely organized as male 

 and female elements. Even where the gametes are 

 different in appearance, so that it is perfectly correct to 

 call them sperms and eggs, some investigators believe 

 that half of the sperms are really female and half of the 

 eggs male. And even if these uncertainties with regard 

 to the gametes were cleared up, there still remains a 

 difference of opinion as to what constitutes union. Some 

 begin to speak of fertilization as soon as the sperm 

 touches the surface of the egg; some regard the entrance 

 of the sperm into the egg as the beginning of fertilization ; 

 many think that the fusion of the two gamete nuclei is 

 the essence of the process; but in some gymnosperms, 

 including the cycads, the nuclei of the two gametes do 

 not form a resting nucleus when they come together. 

 In short, we may define fertilization as the union of 

 gametes, but any attempt to make a more restricted 

 definition, at the present stage of our knowledge, is likely 

 to satisfy only the definer and his friends. 



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