6 



mixture, which, when applied to the vines, destroys the vitality of 

 the spores with which it comes in contact and thus prevents the 

 infection of healthy plants. It should be applied, if possible, 

 before the disease makes its appearance, at least by the last of 

 July, and the applications should be repeated at intervals of ten 

 to fourteen days, and oftener if the mixture is washed off by 

 rains, until the tubers have matured. Usually three applica- 

 tions will be sufficient but a fourth may sometimes be required. 



In experiments made in the summer of 1892, the vines on 

 the sprayed plots remained green from one to four weeks longer 

 than those on the unsprayed plots. 



In one case the yield of merchantable potatoes from the 

 sprayed plot was about one third greater than that from a simi- 

 lar unsprayed plot, while on two other sprayed plots the yield 

 was one half greater than on the unsprayed plot. 



In another case, in a different field, a small sprayed plot 

 yielded three times as many merchantable potatoes as the cor- 

 responding unsprayed plot, while the weight of rotten potatoes on 

 the unsprayed plot was three times as great as on the sprayed 

 plot. 



A photograph of the potatoes from these two plots is repro- 

 duced in Fig. 2, 



EARLY BLIGHT. 



The early blight {Macrosporium solani) has come to be recog- 

 nized as a serious disease of the potato only within the last two 

 or three years. It was first noticed at this station in the sum- 

 mer of 1892. As its name indicates, it makes its appearance 

 earlier than the ordinary blight — by the middle of July or earlier. 

 It first appears, as sharply-defined, rather irregular, dark brown 

 or blackish spots on the leaves. The surface of the spots is 

 usually marked with minute wrinkles, which take roughly the 

 form of numerous circles with a common centre ; this has been 

 called the " target marking," from its resemblance to the con- 

 centric rings of a target. The spots increase gradually in num- 

 ber and size till the whole leaf is destroyed. 



The fungus producing this disease differs considerably 

 in the details of its structure from the late blight, but 



