SEXUALITY OF PLANTS 37 



all ordinary Seed-Plants live on land, and neither the 

 one gamete nor the other is set free into water, nor is 

 motile, it is clear that the mechanism that brings about 

 the fusion of gametes in Flowering Plants must be 

 different from that in the Algae, or in the Ferns. It 

 involves two stages. First the transfer of the pollen- 

 grain from the stamen where it is produced to the recep- 

 tive surface of the stigma : this is called Pollination. 

 The second is the transfer of the male gamete, derived 

 from the pollen-grain, to the ovum with which it fuses : 

 this fusion is called Fertilization, or Syngamy. The two 

 stages are quite distinct in their nature, and should be 

 studied separately. Pollination is only a means to the 

 end : Fertilization is the end itself. 



In Pollination the distance through which the pollen- 

 grain must travel from the stamen to the receptive stigma 

 varies greatly, and depends upon the structure of the 

 flower in question. Some flowers, which are called 

 hermaphrodite, contain both stamens and carpels ; in 

 that case the distance to be traversed may be small 

 (Fig. 15). But in many plants the stamens and carpels 

 may be borne on different flowers, as in the Hazel, 

 Beech, or Oak ; or even on different plants, as in the 

 Campion or Willow. There are thus various degrees 

 of separation of the sexes in the Space which has 

 to be traversed by the pollen-grain. But a separation 

 in Time of maturity is equally a cause of difficulty in 

 pollination, and it may apply even in hermaphrodite 

 flowers. For if the pollen is matured either before or 

 after the stigma of the same flower is ready to receive 

 it, clearly to be effective the pollen must be brought from 

 a distance. Thus pollination is not so simple a problem 

 as it looks at first sight. 



