B. P. I.-27. V '•' '' , - y7 - 



INJURIOUS EFFECTS OF PREMATURE POLLINATION; 



WITH GENERAL NOTES ON ARTIFICIAL POLLINATION AND THE 

 SETTING OF FRUIT WITHOUT POLLINATION. 



INTRODUCTION. 



It is quite generally taken for granted that if pollen is placed on the 

 stigmas of flowers some time before they are receptive it will simply 

 remain there until the stigmas become mature, and then germinate 

 and fertilize the flowers. Darwin." in speaking of the various kinds 

 of flowers with which he experimented in order to show the devitaliz- 

 ing effect of self-fertilization, says: 



As the flowers which were crossed were never castrated, it is probable or even 

 almost certain that I sometimes failed to cross-fertilize them effectually, and that 

 they were afterwards spontaneously self-fertilized. This would have been most 

 likely to occur with dichogamous species, for without much care it is not easy to 

 perceive whether their stigmas are ready to be fertilized when the anthers open. 

 But in all cases, as the flowers were protected from wind, rain, and the access of 

 insects, any pollen placed by me on the stigmatic surface while it was immature 

 would generally have remained there until the stigma was mature, and the flowers 

 would then have teen crossed as was intended. 



Such would perhaps have been the case with some flowers, but the 

 experiments herein described show that it is not true of all. On the 

 contrary, they furnish proof for a statement to the effect that a prema- 

 ture pollination is destructive to the flowers of some plants, prevent- 

 ing them from forming seeds. The experiments and microscopic 

 examinations show that with tobacco at least premature pollination 

 not only results in a failure of the flower to set seeds, but that the 

 growth of the pollen tubes into ovaries before the ovules are mature 

 enough for fertilization results in an injury which causes the flowers 

 to immediately fall. 



The facts that tobacco flowers fall in about thirty-six hours after 

 pollen is applied to the immature pistils, whether the flowers be pre- 

 viously emasculated or not, and that they do not fall if emasculated 

 and not pollinated, nor if pollinated with other pollen than tobacco 



« Cross and Self- Fertilization in the Vegetable Kingdom, p. 23. 



