THE EFFECT OF CEMENT DUST 



(33 



quantity of the cement dust is placed on the stigma, however, 

 it no longer gives this reaction but becomes alkaline due to the 

 lime which is dissolved in the secretions. This is what takes 

 place when the dust from the mills settles over the orchards. 

 What is the effect of this change on germination of pollen? Will 

 pollen germinate at all in an alkaline calcium solution? To de- 

 termine this point, artificial pollen germination tests were made. 

 Pollen germination tests. The method used for germination 

 was this: A definite weight of cement dust, collected from the 

 leaves, was placed in a flask and a measured volume of distilled 

 water added, well shaken and permitted to stand over night, then 



TABLE IV 



Shows results of comparative germination tests of sweet and sour cherry pollen in 

 cement dxist solution and check sugar solutions. Strength of dust solution 1-170 



Cherry pollen 



filtered. After determining the strength of sugar solution re- 

 quired — differing for almost every species tried — the required 

 weight of saccharose was dissolved in the filtrate. Check solu- 

 tions of saccharose of equal strength were made in the same way 

 by using distilled water instead of the dust solution. Pollen 

 from freshly opened anthers was put in drops of these solutions 

 on slides in moist chambers. Checks were always run on the 

 same slide as the tests in order to make conditions the same. 



Cherry pollen. The first artificial germination tests were made 

 during the winter of 1910-11. Twigs of both sweet and sour 

 cherry were brought into the greenhouse and placed in a jar of 

 water, where they bloomed. In testing the pollen thus secured, 





c 



