PHYSIOLOGIC AI, EFFECTS ON PLANTS 15 



ments showed that gas was most injurious to foliage 

 on sunshiny days late in the fall between 9 A.M. and 

 4 P.M. ; that the dormant leaf and fruit buds treated 

 with o. 20 gramme cyanide per cubic foot were not in- 

 jured ; that burned leaves, that is, those injured by 

 the gas, fall readily ; that trees treated in the morning 

 before 9 o'clock and in the afternoon after 4 o'clock, 

 even in sunshine, have the leaves little affected ; that 

 trees treated at night with normal doses do not have 

 the foliage hurt at all. 



On March 18, 1898, experiments were begun upon 

 plum trees, using the same standard dose, just as the 

 buds were unfolding, and observed no injurious effects 

 whatever. June 3, 1898, eight young plum trees, 

 from 8 to 10 feet in hight, were fumigated with o. 16 

 gramme cyanide. The exposure varied from 5 to 12^ 

 minutes, in the sun at 80 F.; in every instance all 

 the lice were killed and the foliage not injured. July 

 8, 1898, three cherry trees were fumigated with o. 16 

 gramme cyanide from 5 to 10 minutes. The trees 

 were infested with the cherry slug. A five-minute 

 exposure did not injure the foliage at all, but did not 

 destroy over 60 per cent, of the slugs; on the other 

 hand, 7^ to 10 minutes destroyed all the slugs, but 

 .severely hurt the leaves. June 13, 1898, two pear 

 trees, badly blighted, were fumigated with 0.20 

 gramme cyanide per cubic foot, for 6 and 10 minutes 

 respectively. We could see no bad effects on the 

 leaves and no decrease in the blight. In April, 1899, 

 after the buds had begun to open, some experiments 

 were completed, using 0.20 gramme cyanide, upon 

 pear trees. The former tests had been made during 



