Mar. 3. I9I9 Development of Vanilla Fruits 251 



It seems quite reasonable to suppose from the heavy fertilization of 

 ovules near the apex and sparse fertilization or entire absence of fertili- 

 zation near the base of the ovary when the vanillon stigma has been 

 pollinated with V. planijolia pollen that these pollen tubes are unable to 

 reach, or reach in only limited numbers the ovules in the far end of the 

 ovary, which are at a considerably greater distance from the stigma than 

 the farthest ovules of the V. planijolia ovary. Even in its own ovary 

 the V. planifolia pollen causes a much heavier fertilization near the apex 

 than near the base. This inability of V. planifolia pollen tubes to reach 

 the farthest ovules was particularly marked when V. planifolia pollen 

 was applied to V 43, which is one of the largest flowered of the vanillon 

 varieties. 



The vanillon pollen tubes, however, reach ovules in the V. planifolia 

 ovary at a much shorter distance from the stigma than in their own 

 flower. Many of these first ovules which the V. planifolia pollen would 

 fertilize are left unfertilized by the vanillon pollen, the pollen tubes pass- 

 ing by to other ovules which are nearer the normal distance from stigma 

 to ovary in the vanillon flower, and causing a much heavier fertilization 

 in the base of the pod than w^ould the V. planifolia pollen. 



This might possibly indicate in this instance the necessity for a certain 

 maturity of development of the pollen tube before the ovule can be 

 fertilized. 



