182 



PLANT STRUCTURES 



little drift at the bottom of each carpel, where the ovules 

 are found (Fig. 147, A, B). The flaring lips of the micro- 

 pyle roll inward and outward as they are dry or moist, and 

 by this motion some of the pollen-grains are caught and 

 pressed down upon the apex of the nucellus. 



In this position the pollen-tube develops, crowds its 

 way among the cells of the nucellus, reaches the wall of 

 the embryo-sac, and penetrating that, reaches the necks 

 of the archegonia (Fig. 149, p, t) ; crowding into them 

 (Fig. 151), the tip of the tube opens, the male cells are 



sn 



Pig. 152. Fertilization in spruce (Picea): B is an egg, in the tip of which a pollen 

 tube (p) has entered and has discharged into the cytoplasm a male nucleus (sn), 

 which is to unite with the egg (female) nucleus (on); C, a later stage in which the 

 two nuclei are uniting. — After Schimper. 



discharged, one male cell fuses with the egg (Fig. 152), 

 and fertilization is accomplished, an oospore being formed 

 in the venter of the archegonium. 



It will be noticed that the cell which acts as a male 

 gamete is really the sperm mother cell, which does not 

 organize a sperm in the absence of a water connection. 

 This peculiar method of transferring the male cells by 

 means of a special tube developed by the antheridium is 



