228 



THE MONTHLY BULLfiTlM. 



to kill, considerable preliminary work was done, first in cans, then in 

 tubs and later in 2 by 5-foot plots in the open field. It was found that a 

 very small dose of cyanide would do the work, provided it was put in 

 the soil below the worms and the top of the ground packed to hold the 

 gas. The kill in every case was slow, requiring from 3 to 7 days. In 

 each case the cyanide was put in 8 inches deep in a single row in the 

 center, running lengthwise with the plot, the ground being thoroughly 

 tramped on top to hold the gas. In every case the only worms found 

 alive were those along the outer edges of the plot and below the action 

 of the cyanide. To get the percentages given below, all the worms 

 found in a space 1 by 2 by 5 feet were counted. The following table 

 summarizes the results obtained on the 2 by 5-foot plots in the open 

 field: 



It will be noticed that there is practically no difference in the action 

 of cyanide in solution and that used in the powdered form. At this 

 point the liquid solution was discarded on account of presenting more 

 difficulty in applying. There is comparatively little difference between 

 the results obtained with the stronger doses and with the weaker ones. 

 Experiment 7 was put in after the results of the first six were known, 

 and the good results obtained were attributed to the fact that the 

 ground was more thoroughly packed. All the preliminary experiments 

 were carried on in a medium loam. 



The following diagram will give an idea as to the killing range of 

 cyanide gas : 



xop of groimd 



1 ft. 



8 in. 



\ 



cyanide 

 4 in. / 



1 ft, 



Fig. 76. — Dia^am showing killing range of cyanide gas. (Original.) 



Nine-tenths of the live worms were found in the corners. It will be 

 noticed from the diagram that there is a considerable killing area below 

 where the cyanide was actually placed. 



As the season was growing late, these experiments were discontinued, 

 and a trial in the field given. The soil picked for this was very light 

 and sandy. Owing to the difficulty in packing, it was thought that this 

 soil would furnish as severe a test as it would be possible to give. 

 Through the work with the potato catch-crop it was learned that worms 

 could be attracted considerable distance to bait, so split beans were 



