FUMIGATION AGAINST THE PURPLE SCALE. 



41 



scope of the schedule, the hmits were made very broad. From the 

 difference in strength of kiUing dosage between these three experi- 

 ments we would be able to determine the effect of length of exposure 

 on results secured. 



To obviate as much as possible the leakage of gas, which would vary 

 in trees of different sizes, trees were chosen of as uniform a size as 

 could be obtained. The cubic contents of the trees chosen for the 

 first two experiments did not vary greatly and the trees ranged 

 between 11 and 14 feet in height. As in the first two experiments 

 most of the larger trees had been used, for the third experiment we 

 were compelled to utilize those remaining, which varied somewhat 

 in size, and were also, for the most part, noticeably smaller than 

 those represented in the first two experiments. 



During the latter part or January an examination was made of the 

 results of these experiments. Fully two weeks were devoted to this, 

 and thousands of the purple scale were scrutinized. The method 

 employed was a very careful one. In each case the scales were 

 overturned and examined with a powerful hand lens. In those 

 instances in which the entire contents of the scale were not at once 

 revealed, the delicate ventral scale was ruptured and the contents 

 scraped out. Through this method not a single egg could escape 

 observation. 



Four trees were used in each test and an examination to deter- 

 mine results was made of each. This examination included many 

 infested leaves and branches taken as close to the ground as possible 

 and up to 6 or 7 feet above the ground. Infested fruit was also 

 examined when obtainable. The average condition existing in these 

 four trees was taken to indicate the result ot the test. 



The chemicals were used in the following proportion: Potassium 

 cyanid, 1 part; sulphuric acid, 1 part; water, 3 parts. 



Table IY .—Fumir/ation for the purple scale, experiment No,. 1. 

 [Length of exposure, thirty minutes; height of trees, 11 to 14 feet.] 



