ARSENATE OF LEAD AGAINST TOBACCO HORNWORMS. 7 



quired. Experiment No. 2, 4 pounds of arsenate of lead per acre, 

 was more effective than the 2^ pounds of Paris green. Although a 

 considerable number of worms were left on plat 2, we find that fewer 

 were alive in this experiment on the fourth day than were alive in 

 the Paris green experiment, notwithstanding the fact that there were 

 practically 20 per cent more worms on No. 2. the arsenate of lead 

 plat, at the time of application of the poison than there were on the 

 Paris green plat. Fortunately for the effect upon the tobacco plants, 

 the rain washed off nearly all the Paris green, so that there was very 

 little burning. There was no burning of plants on the arsenate of 

 lead plats. 



Table III. — Comparison of insecHcidal effect of good and poor applications of 



arsenate of lead. 



1 On 200 plants. 



In Table III, which gives a comparison of a good and a poor a im- 

 plication of arsenate of lead, application No. 1, 4^ pounds arsenate 

 of lead per acre, was from the same keg as application No. 2, ;U 

 pounds per acre. Counts were made on 50 hills in each instance. 

 On August 16, 1910, many eggs were noticed on the plants, so that 

 most of the worms appearing on this plat were small. It will be 

 noticed that the application did not keep down the increase of worms 

 due to hatching. In experiment No. 2 there were very few eggs on 

 the plants and the worms were therefore larger than on plat 1 and 

 harder to kill. Practically a clean sweep was made on No. 2, only 

 14 worms being found on 200 plants on the fourth day after the 

 application. Favorable weather prevailed after both applications, 

 and the conditions at the time of application to both plats were 

 equally favorable. What, then, is the explanation of the poor results 

 on plat 1 and of the very excellent results on plat 2? The explana- 

 tion is found in the carrier. In No. 1 the arsenate of lead was mixed 

 thoroughly with an equal weight of finely sifted air-slaked lime, 

 while in No. 2 it was thoroughly mixed with an equal weight of 

 finely sifted dry wood ashes. Notwithstanding the dryness of the 



