90 



80UTBEBN FIELD CROPS 



tnsi. 



Hence, fields of two different varieties of corn, which 

 the farmer desires to keep unmixed, should not be planted 

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

 each other, xmless 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 supplying of food or 

 fertilizing material to the plant. 

 Fertihzation of the flower consists 

 in the growing of the pollen-tube 

 t 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 imion, 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, pollen-tube which silk and through its entire length to 

 nX*?frig"e^u the point where the silk originates, 

 which, after union with There the pollen-tube enters the 

 one of the male elements, gmbryo-sac and sets free two male 



lorms the germ ; end., nu- 



eleus of the endosperm, nuclei. One of these Unites with the 

 with which the second egg-cell, effecting true fertilization 



male nucleus may unite. , i . ,, « ,, 



(Drawing by F. E. Lloyd.) and producmg the germ of the gram; 



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 



Fig. 37. — The Embryo- 

 sac IN Corn at the 

 Time of Fertilization. 



