FLOWERS: POLLENATION AND FERTILIZATION 113 



The pollen grain from the anther and the ovule in the ovary 

 are actually the most necessary factors in the process of reproduc- 

 tion and must now be dealt with more completely. 



FIG. 36. Seed Development. 



Part I. Pollenation 



Fig. 1. The stamen is shown with part of the filament, and the anther open- 

 ing to set free the pollen. This may be transported either-by wind or insects, 

 to the stigma of the pistil of a similar kind of flower, shown in Fig. 2. 



After arriving there, the pollen develops a long tubular cell which reaches 

 clear to the ovary, down the whole length of the style, even though it be as 

 long as a "silk" of corn. 



The development of this tube, and the passage of the sperm nucleus from 

 the pollen, down it, are shown here, though they are really steps in fertilization. 

 Pollenation is really the mere transfer of the pollen. 



Part II. Fertilization. 



Fig. 1. The pollen tube is entering the micropyle and the sperm nucleus is 

 at its lower end. Note the ovule nucleus, with which it is to unite. Both one- 

 celled stages. 



Fig. 2. The sperm nucleus has passed out of the pollen tube and is approach- 

 ing the ovule nucleus. 



Fig. 3. The sperm and ovule nuclei have united; this is the actual fer- 

 tilization, from which the development of the embryo begins. 



Fig. 4, 5 and 6 show stages in the early cell divisions as the embryo develops. 



Fig. 7 shows the matured seed. The parts of the embryo have gone as far 

 as they will till germination commences. Extra stored food remains unused 

 outside, as endosperm. 



