GENERAL STRUCTURE 



275 



cates the number of carpels of which the pistil is composed. 

 (See Figure gy.) 



c. Fertilization. — It is within the ovule that the sex 

 process occurs. It is here that there develops that hidden 

 generation which the pollen tube 

 seems to seek and finds. That hidden 

 generation produces a cell called the 

 egg. The pollen tube contains two 

 cells called sperms. (See Figure qq.) 

 Sperms are male cells. The egg is a 

 female cell. Both are sex cells, or 

 gametes. The egg and one of the 

 sperms unite. This union of egg and 

 sperm is called fertilization. Fertili- 

 zation occurs within the ovule. (See 

 Figure Q5.) It is the sex process. It 

 has already been described as the union 

 of " portions from the bodies of sepa- 

 rate parents." (See page 58.) As 

 you now see, the portions referred to 

 are the sperm and the egg. The cell 

 which results from the fusion of egg 

 and sperm is called the fertilized egg. 

 The fertilized egg develops into the 

 embryo. (See Figure gg A.) 



Fertilization is, you see, a very dif- 

 ferent thing from pollination. Polli- 

 nation takes place on the stigma. Fertilization takes place 

 within the ovule. The growth of the pollen tube separates 

 them. The pollen tube must grow down the style and 

 reach an ovule before fertilization occurs. (The difference 

 between pollination and fertilization is thus emphasized 



Fig. 99. — The germina- 

 tion of a pollen grain, 

 the pollen tube being 

 well developed. Much 

 magnified. Si and St 

 are sperms. 



