A STUDY OF THE POLLEN AND PISTILS OF APPLES 



IN RELATION TO THE GERMINATION OF THE 



POLLEN. 



J. N. MARTIN AND L. E. YOCUM. 

 INTRODUCTION. 



T'he failure of a fruit tree to develop a normal amount of 

 fruit may be due to a number of causes as stated b'y Kraus in 

 volume VI of the Journal of Heredity. However, unless a plant 

 develops fruit parthenocarpically, the development of fruit de- 

 pends primarily upon how the pollen and pistil function relative 

 to each other. As Kraus points out, fertilization by no means 

 insures the development of a fruit, for very commonly the fruit 

 does not develop despite the fact that normal fertilization oc- 

 curred, but, on the other hand, in the absence of fertilization, 

 fruit seldom develops among apples. 



The aim of the work reported in this paper was as follows: 

 (1) to determine the content of the pollen; (2) to investigate 

 the germination of the pollen in solutions and on membranes 

 with a view to discovering the requirements of the pollen for ger- 

 mination; (3) to determine the effects of different temperatures, 

 of age, and of drying on the germination of the pollen ; (4) to 

 determine the structure and content of the stigma and style, 

 whether or not secretions are present on the stigma, and the be- 

 havior of the stigma with reference to the germination of the 

 pollen. 



It was thought that such investigations might give some in- 

 formation concerning: (1) the effect of rainy weather during 

 the blooming period on the setting of fruit; (2) the condition of 

 the stigma at the time horticulturists regard it as receptive; (3) 

 the time at which artificial pollination can be done most success- 

 fully; and (4) whether or not the bagging of flowers practiced 

 by horticulturists in experiments involving artificial pollination 

 has any effect upon the results of pollination due to increasing 

 the moisture content of the air about the flowers. 



It is claimed by some that rains during the blooming peria*.! 

 prevent the pollen from functioning properly by washing away 

 or diluting the stigiiiatic secretions. The glistening of the stigma 

 at the time it is considered receptive is interpreted by some as 

 due to the presence of a secretion. If apple flowers can be suc- 

 cessfully pollinated at the time they are emasculated then much 



