Poly gala poly gam a and P. panciflora. 141 



existence of the species in case sexual reproduction, depend- 

 ing on favorable outward conditions, failed. 



Darwin,' quoting Delpino, regards his view to a certain 

 extent as correct. He points out that a majority of plants 

 which produce cleistogamic flowers, have their evident ones 

 adapted for fertilization by insects, and that during certain sea- 

 sons, through scarcity of insects, these would fail to be fer- 

 tilized, and so there would be a failure of seed production, 

 unless this were accomplished by some other means. " It 

 is difficult to avoid the belief that the production of cleis- 

 togamic flowers, which ensured under all circumstances a full 

 supply of seed, has been in part determined by the perfect 

 flowers being liable to fail of their fertilization." But he imme- 

 diately makes it clear that he does not consider that this is the 

 chief reason for the development of cleistogamic flowers. He 

 points out that wind-fertilized genera also produce such, and 

 says further of the causes of cleistogamy: " The production 

 of a large supply of seeds with little consumption of nutrient 

 matter and expenditure of vital force, is probably a far more 

 efficient motive power. The whole flower is much reduced in 

 size ; but what is more important, an extremely small quan- 

 tity of pollen has to be formed, as none is lost through the 

 action of insects or the weather, and pollen contains much 

 nitrogen and phosphorus." And seeing that they possess 

 this advantage, he thinks that if any cause prevented a plant 

 from completing the development of its flower, natural selec- 

 tion would step in to preserve this advantage and so lead to 

 the production regularly of cleistogamic flowers. 



Mr. S. Le M. Moore" criticised Dar%vin's views on cleisto- 

 gamy, basing his opinions on a few observations of Vegetable 

 Marrow. He points out that conspicuous flower-parts 

 quickly wither after pollination, and suggests that if poUina- 



' Darwin. Forms of Flowers, p. 339. 

 'Trimen. Jour, of Bot., iSSi, p. S4, 



