74 PLANT-LIFE ON LAND [CH. 



pollen shall be landed upon the surface of the stigma 

 (Fig. 15, p. 73). Thus the more hazardous part of the 

 journey is accomplished, with or withotit intercrossing. 

 Then begins the further development of the pollen- 

 grain. A delicate tube grows out from it, which 

 penetrates the tissue of the style, and makes its 

 way downwards to the cavity of the ovary. Finally, 

 it reaches the apex of the ovule, and comes into 

 close contact with the egg-apparatus. This tube 

 conveys the contents of the pollen-grain, so that the 

 transfer to the deeply seated egg, otherwise difficult, 

 is readily accomplished. When the germination of 

 the pollen-grain upon the surface of the stigma 

 begins, the contents of the grain pass into the 

 tube. The antheridial cell divides into two gametes 

 (g, Fig. 14), and these preceded by the vegetative 

 nucleus (k, Fig. 14), maintain a position near to the 

 apex of the tube as it grows. Finally, on reaching 

 the embryo-sac, the nucleus of one of the gametes 

 enters the ovum, and fuses with its nucleus. This is 

 the essential point in fertilisation. The resulting cell, 

 or zygote, forms the starting-point for development 

 of the new individual. Since the nucleus is believed 

 to be the bearer of hereditary qualities, the zygote 

 will have received those of both parents, so far as 

 they are conveyed by the nuclei which coalesce ; 

 and those qualities will pass on to the newly produced 

 offspring. 



