CH. VI, 4] NATURE OF FERTILIZATION 



279 



ordinarily wither and fall away, 

 leaving only the ovary on t,hf> ra- 

 fifvp tn.fi Ifi. Then tnis ovary grows 

 inio a fruit, the ovulainto a se( 



fl.nH tbft fprtili/eH egg cell into an 

 embrY n plant In case, however, 

 no fertilization is effected, the parts 

 of the flower usually persist some- 

 what longer than otherwise, though 

 no fruit, seed, or embryo is 

 formed; but presently all parts, 

 including the ovary, wither and 

 fall. This is the way in which 

 flowers are essential to the pro- 

 duction of seed. 



4. THE NATTTRJTC AND 



Fertilization in flowers, as the 

 preceding section has shown, cen^, 

 in the fusion of the male anc] 



____________________ FIG. 192. The fusion of 



female nuclei within the egg cell : the sex cells somewhat gen- 



- n M " "' n " '/. eralized from a typical case ; 



lor pollination and the growth of x 375. 



the pollen tube are merely the A* the end of the pollen 



, . . , . . tube (D of Fig. 188), contain- 



mechanism tor bringing the sex ing two -sperm nuclei, sk ; B, 



cells together. Fertilization occurs the same tube in contact with 



. , , ^T- . -, r, an embryo sac, en ; C, a sperm 



4nthe reproduction ot nearl^aJL nucleus> skt has entered the 



plants and animals, and while the 



- - - - 



e % cell > the nucleus of which, 



- -s - s r* . ek, it has approached ; D, the 



mechanisms tor bringing the sex sper m nucleus, sk, has lost its 



Cells together are as diverse as elongated form and become 

 ., , ., ,, rounded like the egg nucleus, 



possible,, the central feature of the with which next it fuses com- 



pletely. 



(Reduced from Stras- 



jusion, especially of the nuclei T is 

 always the same. Thus this fusion 

 acTbf fertilization ^runs as a thread of structural and physi- 

 ological identity almost throughout the plant and animal 

 kingdoms, binding plants and animals together in this 



