CHAPTER XXXII 

 POLLINATION OF FLOWERS AND PROTECTION OF POLLEN 



393. Topics of the Chapter. The ecology of flowers is con- 

 cerned mainly with the means by which the transference of 

 pollen, or pollination, is effected, and with the ways in which 

 pollen is kept away from undesirable insect visitors and from 

 rain. 



394. Cross pollination and self pollination. It was long sup- 

 posed by botanists that the pollen of any bisexual flower needed 

 only to be placed on the stigma of the same flower to insure sat- 

 isfactory fertilization. But in 1857 and 1858 the great English 

 naturalist, Charles Darwin, stated that certain kinds of flowers 

 were entirely dependent for fertilization on the transference 

 of pollen from one plant to another. It was also shown that 

 probably nearly all attractive flowers, even if they can produce 

 some seed when self-pollinated, do far better when pollinated 

 from the flowers of another plant of the same kind. 1 This im- 

 portant fact was established by a long series* of experiments 

 on the number and vitality of seeds produced by a flower when 

 treated with its own pollen, or self-pollinated, and when treated 

 with pollen from another flower of the same kind, or cross- 

 pollinated. 2 



Another important advantage of cross pollination is that it 

 tends to give the offspring additional variability (Chapter XL), 

 and thus enables them better to adapt themselves to changing 

 environment or to any difficult conditions. 



1 See Darwin, Cross and Self Fertilization in the Vegetable Kingdom 

 (especially Chapters i and n). 



2 On dispersion of pollen, see Kerner and Oliver, Natural History of 

 Flams, Vol. II, pp. 129-287. 



420 



