90 



SOUTHERN FIELD CROPS 



Hence, fields of two different varieties of corn, which 

 the farmer desires to keep unmixed, sliould not he planted 

 at ebout the same date, within less than half a mile of 

 each other, unless there be intervening woods or other 

 obstacles to the blowing of the pollen. 



90. Impregnation or fertilization of the grain. — The 

 word "fertilization," as used in this paragraph, does not 

 refer to the supplj-ing of food or 

 fertilizing material to the plant. 

 Fertilization of the flower consists 

 in the growdng of the ]iolIen-tube 

 i along the entire length of the 

 silk and into the embryo-sac (Fig. 

 36), and its union there with the 

 egg-cell of the mother plant to 

 produce the seed (Fig. 37). With- 

 out such a union, no seed is 

 formed. 



After the pollen-grain has lodged 

 on the sticky surface of the protrud- 

 ing end of the silk, it grows into that 

 pt., polien-tuiDe which silk and through its entire length to 



has just discharged 2 male .-i ■ , ^ ,, ■,, . .'^ . 



nuclei, cT; 5, egg -cell ^^^ P^"^* ^^'^ere the silk origmates. 

 wiiich, after union -nith There the pollen-tube enters the 



one of the male elements, 



Fig. .37. — The Embeyo- 

 sac in cohn at the 

 Time of Fertilization. 



forms the germ ; end., nu- 

 cleus of the endosperm. 



embryo-sac and sets free two male 



nuclei. One of these unites with the 



with which the second egg-cell, effecting true fertilization 



male nucleus may unite. 



(Drawing by F. E. Uoyd.) and producing the germ of the grain ; 



the other male nucleus unites with 



the nucleus of the endosperm (Fig. 37). When this second 



union occurs, the result is an endosperm that derives 



