THE EFFECT OF CEMENT DUST 



61 



Dusting experiments. During the blooming season of the next 

 year (1911) the mills were temporarily closed. Therefore it 

 was necessary to depend on artificial dusting for our experiments. 

 This however was really an advantage since it offered the oppor- 

 tunity of having dusted and untreated check blossoms all on the 

 same tree, making the conditions entirely equal Sweet cherry, 

 sour cherry, pear and apple trees were used. Two branches 

 were selected from each tree which were as near alike in size, po- 

 sition, etc. as could be found. Cement dust, which had been 

 collected from foliage the previous summer and had been kept 

 in air-tight bottles, was blown over the blossoms of one of the 

 branches as soon as they opened, while the blossoms on the other 

 branch were left untreated. When the fruit was about half 



TABLE III 

 Shows the luunber of treated and untreated fruit blossoms which set fruit 



Sweet cherries. 

 Sour cherries. . 



Pears 



Apples 



PER CENT 



32 .93 

 65.16 

 18.43 

 49.90 



grown, the number which had set on each branch was counted. 

 The cherries and pears were dusted twice each day; the apples 

 on the other hand, only at irregular intervals. The results from 

 the latter are included in the table below to show that even an 

 occasional dusting is injurious. In each case, ten to twenty 

 branches were treated, but in the table, the total number of 

 blossoms is given for all the branches that received the same 

 treatment. 



From Table III it will be seen that only a very small percent- 

 age of the blossoms that had dust blown over them set fruit. 

 It will be asked why any of the fruit at all set when the blossoms 

 were all dusted. In the first place, all of the blossoms may not 

 have been reached by the dust. In the second place it is known 

 that the growth of the pollen tube is very rapid in warm weather 



