200 RZPOHT OF THE B0TA2fICAL DEPARTMENT OF THE 



sulphur can be profitably substituted for bordeaux mixture in the 

 spraving of potatoes. Both lack the stimulative influence' pos- 

 sessed by bordeaux and, besides, lime-sulphur has a tendency to 

 d"warf the plant* and lower the yield. However, it will be neces- 

 sary to repeat this experiment several times before the relative 

 e^ciency of the different spray mixtures can be definitely stated. 

 The differences obtained in this experiment are undoubtedly 

 extreme. 



Under other conditions the results might have been very dif- 

 ferent. The unusually long growing season (158 days) gave the 

 bordeaux an opportunity to exert its influence to the full extent. 

 Had the plants been killed by frost about October 1, as frequently 

 happens, the differences in yield would have been much smaller. 

 Also, had the spraying been less thorough there would have been 

 less benefit from the bordeaux and less injury from the lime-sul- 

 phur. In light applications, such as are commonly made by 

 farmers who use horse-power sprayers, the injurious effect of the 

 lime-sulphur would probably not be great enough to attract atten- 

 tion. Had there been a severe attack of blight the results might 

 have been different. The value of lead benzoate and lime-sulphur 

 for the prevention of potato blight is yet unknown, but it is 

 improbable that either is superior to bordeaux mixture for this 

 purpose. 



PosTSCBiPT. — Since this bulletin was written we find in the Journal of the 

 Department of Agriculture and Technical Instruction for Ireland (Vol. XII, 

 Xo. 2. Jan.. 1912 >, an account of an experiment made bv Dr. Pethybridge 

 in Ireland. In this experiment three applications of lime-sulphur solution 

 (dilution not stated i proved utterly useless as a preventive of blight 

 ( Phytoph thora infestans ) . 



1 Although unable to explain the process, phvsiologically, the writers are 

 confident that bordeaux preserves the foliage, prolongs the life and increases 

 the yield of potato plants even in the absence of parasitic organisms. The 

 experiment reported in this bulletin is only one of several in which we have 

 observed what we consider evidence of the stimulative influence of bordeaux. 

 While this view is held bv manv experimenters there are some who dispute it. 

 (See article bv O. Kirchiier in Ztschr. Pflanzenkr. 18:65-81. 1908.) 



