SOCIETY OF NORTHERN ILLINOIS. 321 



notice that only a third of an inch of rain had fallen between the 

 last spraying and the picking of the fruit. Weed concludes that 

 spraying may be continued until within three or four weeks of 

 ripening. 



Cook has made some careful experiments with respect to the 

 poisoning of pasture under the trees sprayed — some chemical and 

 others practical. First carefully cutting the grass under a large 

 tree which had been heavily sprayed with a mixture of twice the 

 usual strength, he found by analysis that 2.2 grains of arsenic had 

 been sprayed upon this grass, about one-fifth the poisonous dose 

 for a cow and one-tenth that for a horse. In a similar experiment 

 he cut the grass under a tree and fed it to his horse without any 

 subsequent sign of injury. Three sheep were similarly treated 

 with the same result. I cannot, however, endorse the conclusion 

 reached by Cook that these experiments conclusively prove that 

 there is no danger to stock from the poisoning of pasturage. 

 Arsenic is a cumulative poison, and a daily feeding for two or 

 three weeks upon grass which had been sprayed with arsenites 

 might have very different consequences from a meal or two. 



In this connection, it may be well to note the poisonous doses 

 of these substances for man. They vary, for arsenic, from one- 

 eighth to one fourth of a grain for a two-year-old child, to one or 

 two grains for an adult, the corresponding fatal doses for Paris 

 Green and London Purple being two or three times as much. 



Although not strictly related to my subject, I will not close 

 without calling attention to an important matter with respect to 

 the uses and effects of these insecticides contained in Bulletin 

 No. 10 of the Division of Entomology of the U. S. Department of 

 Agriculture, published in 1887, the subject being "Our Shade Trees 

 and their Insect Defoliators." Particularly interesting, from our 

 point of view, are the differences in effect produced upon dif- 

 ferent trees of the same species, the various methods described 

 for the preparation and application of the poisons, the elaborate 

 illustrations of the apparatus used, and the comparative notes 

 with respect to the effects of the different poisons under 

 experiment. 



BORDEAUX MIXTURE. 



The numerous objections to the use of the arsenites in the- 

 apple orchard give particular interest to any hint of a less dan- 

 gerous substitute. The so-called Bordeaux mixture, essentially 

 blue vitriol and lime suspended in water, has come into promi- 

 nence as a fungicide, and has been lately used in a spray upon 

 trees to prevent the formation of the scab of the apple and the 

 rot of the plum. Its effect to check mildew of grape is well 

 known to horticulturists. Observations made by Lugger, of 

 Minnesota, and Garman, of Kentucky, make it likely that it will 

 be found to have an insecticide value also. Weed, of Ohio,. 

 —22 



