278 



A TEXTBOOK OF BOTANY 



[Cn. VI, 3 



enzymes and absorbing the digested products for use in its 

 own further growth; and commonly the tiibe_dies^and 

 withers behind as the forward part advances^ Thus it 

 reaches and enters the ovary, and, taking a direct path, 

 approaches an ovule which it enters by thp jn^nrnpylar 



Gagging ; thus it reaches the rela- 

 tively large sac, the embryo sac, 

 which every ovule contains (Fig. 

 190), and within which, near the 

 micropyle, lies the EG^CELL. This 

 mechanism of fertilization is repre- 

 sented in principle in our general- 

 ized picture (Fig. 191). Thus_ 

 the sperm cellsjjrought to thejm- 



vicinity of the egg cells. 



The final, and really the essen- 

 tial, stage in this process consists 

 in the fusion of the two sex cells 

 <arhich is^thus effected (Fig. 192). 

 One of the two male nuclei (the 

 of the other will appear later 



in connection with the fruit), with 

 probably some surrounding cyto- 

 plasm, .moves out of_tb R pnllpp 

 tube into the egg cell, presumably 

 opening the way by action of 

 enzymes. For a time the egg cell 

 exhibitsJTvvo micleij but they move 

 together, touch, and then gradually 

 fuse together into one and fertili- 



zation is complete. ^The result is a cell crmtflininffa, nucleus 

 derive^ f m f he union of two nuclei from different parent 



FIG. 191. A generalized 

 pistil and ovule, in section, 

 showing the mechanism of fer- 

 tilization described in the text. 



and this appears to be the central and essential feature 

 of all fertilii 



ter fertilization the sepals, petals, stamens, nectaries, 

 styles, and stigmas, their functions evidently accomplished, 



