270 Funf/icidal Properties of Certain Sprnij-Flidih. 



patches of <S'. Humuli were selected for spraying on one leaf at a node, 

 while the similar patches of mildew on the other leaf at the same node 

 served as "controls." 



The experiments carried out fall into two classes: viz. (1) those in 

 which arsenical solutions were used; and (2) those in which lime-sulphur 

 or its constituents were used. 



1. Experiments with Solutions containing Arsenic. 



Several investigators have stated from time to time that arsenic 

 possesses some fungicidal power. Waite(:)), who appears to have been 

 the first to have discovered this, stated in 1910 that arsenate of lead 

 "seems to possess considerable fungicidal value, though probably not 

 enough to be depended upon for general use." Similar statements have 

 been made by Cliuton( l) and Watkins(5). Wallace, Blodgett and Hesler(6) 

 considered that arsenate of lead was "about as effective as lime-sulphur" 

 in controlling apple-" scab" (Venturia inaequalis) in the orchard; but 

 state that in laboratory experiments with germinating spores of apple- 

 "scab," "brown rot" and Sphaeropsis, arsenate of lead was found to 

 have only "a weak fungicidal value." Morse has repeatedly claimed 

 fungicidal powers for arsenate of lead; in 1914 he stated(7) that "arsenate 

 of lead paste controlled apple scab as well as Bordeaux mixture and lime- 

 sulphur," and, from observations made on trees in sprayed orchards, 

 that "even small or medium applications of arsenate of lead possess a 

 distinct fungicidal value"; in 1915, the conclusion was drawn(S), again 

 from observations made in sprayed orchards, that "arsenate of lead was 

 less efficient in controlling scab than the standard fungicides, but still 

 noticeable." In 1916 Morse stated(!i) that arsenate of lead alone controls 

 apple-" scab" on the fruit (apple) as well as, or better than, lime-sulphur 

 mixed with arsenate of lead, but added that "laboratory experiments 

 by Mr M. Shapovalov failed to show for arsenate such high fungicidal 

 properties as the field experiments indicated. Germination of conidia 

 of the fungus {Venturia inaequalis) placed in similar dilutions of the 

 poison was reduced and retarded, but by no means prevented." In 1918, 

 Morse, in recording(io) the results of spraying experiments in apple 

 orchards, stated that "the use of arsenate of lead alone as a spray re- 

 duced the amount of scab on the foliage from 90 to 95 per cent." Sanders, 

 in 1917, from spraying trials made in the orchard, recorded(H) that "the 

 arsenate of lime alone seems to be almost as valuable a fungicide as the 

 arsenate of lead alone." On the other hand, the .statement has been made 

 by Pickett(i2) that arsenate of lead has practically no fungicidal value. 



