44 LEAD ARSENATE. 



or turn yellow. In very minute quantities arsenic appears to exert 

 a stimulating effect or act as a tonic, as it does on animals. It is 

 probably this action which, by accelerating the functional activity 

 of the leaf and producing more rapid assimilation, causes the excess- 

 ive reddening and hastens the maturity of the fruit. On the other 

 hand, if too large an amount is absorbed, it has a toxic effect, resulting 

 in retarded assimilation, which in turn will cause the fruit to shrivel 

 and drop before it has matured. 



SUSCEPTIBILITY OF PEACH FOLIAGE TO INJURY. 



It has not been satisfactorily explained why the stone fruits, the 

 peach in particular, should be so susceptible to injury. Numerous 

 investigators have carried on extensive experiments on this point 

 with copper compounds, mostly Bordeaux mixture, and with Paris 

 green, resulting in much valuable information on the subject and the 

 advancement of several theories to account for it. Those who have 

 given special study to the action of fungicides and insecticides on 

 plants and foliage include numerous foreign investigators. Among 

 those in this country the following may be mentioned : Gillette, a 

 Galloway, b Galloway and Woods, c Fairchild, d Sturgis, e Bain, / and 

 Hedrick. ff 



It has been shown that leaves formed in a moist atmosphere have 

 a thinner and more easily permeable cuticle than those grown in a 

 dry atmosphere, and that injury from Bordeaux mixture and arsen- 

 icals is more severe in warm, damp weather. Gillette * says: "The 

 oldest leaves are most susceptible to injury;" also, "foliage most 

 exposed to dew and direct sunlight will be most injured by the 

 arsenites, other things being equal. Leaves kept perfectly dry can 

 hardly be injured by the arsenites." Woodworth and Colby:*' "It 

 has been demonstrated repeatedly that dry Paris green can be placed 

 upon a leaf in any quantity and so long as the leaf remains dry no 

 evil results will follow." 



No experiments have been made in this investigation with lead 

 arsenate to determine whether or not injury would result to peach 

 foliage in the absence of water. It was assumed that none would 

 be caused, in view of the results obtained by others with Paris green, 



<* Iowa Agr. Exper. Sta., 1890, Bui. 10. 



b U. S. Dept. Agr., Div. Veg. Path., 1892, Bui. 3; 1894, Bui. 7. 



c Proc. Soc. Prom. Agr. Sci., 1895, p. 42. 



<* U. S. Dept. Agr., Div. Veg. Path., 1894, Bui. 6. 



Connecticut Agr. Exper. Sta., Ann. Rep., 1900, Pt. Ill, p. 219. 



/Tennessee Agr. Exper. Sta., 1895, Vol. 8, No. 3; 1902, Vol. 15, No. 2. 



g New York Agr. Exper Sta., 1907, Bui. 287. 



fclowa Agr. Exper. Sta., 1890, Bui. 10, pp. 402-403. 



* California Agr. Exper. Sta., 1899, Bui. 126, pp. 10-11. 



