152 THE NATURE AND WORK OF PLANTS 



207. Fertilization. — When the pollen is carried 

 to the flower which it may benefit, it can only be of 

 use if it is deposited on or near the stigma at the top 

 of the pistil. Here it finds a sweetish and sticky 

 substance made up of cane sugar and glucose which 

 it uses as food in any growth it may make. If 

 properly placed on this stigma, the presence of this 

 sweetish substance starts it to germinating. A long 

 slender tube is produced, making a structure much 

 as if the head of a pin were to grow out and form 

 the body of the pin. The pollen tube is generally 

 very crooked and it bores into the sticky substance 

 in which the pollen grain is imbedded, and then 

 grows down into the style in an effort to get away 

 from the oxygen of the air. Not only does it strive 

 to get away from the oxygen of the air, but certain 

 substances in the ovary attract it. Now the tube 

 formed by the grain or pollen is a part of a gameto- 

 phyte, and near its tip it contains a minute mass of 

 protoplasm, which is the male gamete which is to 

 be carried to the egg. The embryo sac in the 

 ovary contains the female gametophyte bearing an 

 egg cell, and the pollen tube extends to it, carry- 

 ing the male gamete in its own tip. The union of 

 the gamete from each constitutes fertilization, and 



