Diseases of the Potato. 307 



of direct sunlight and rainfall, the plants growing under the trees 

 are in practically the same condition as those growing within the 

 area occupied by the feeding roots of the tree. They have about 

 the same amount of soil moisture and of heat, and they also suffer 

 to nearly the same extent from injury by insects. But they escape 

 the moisture of light showers, and they are also free from dew. 

 It appears probable, tnerefore, that the secret of their immunity 

 from disease lies in this fact. 



Although the character of the season exerts a great influence 

 upon the prevalence of early blight, it is not the only great factor 

 which has the power of seriously reducing the vitality of potato 

 plants. A second agent is a small organism which often appears 

 in countless numbers. It is generally known as the flea-beetle, 

 on acount of its quick movements when disturbed. The injury 

 done to the foliage by these little beetles is greater than was 

 formerly supposed. They feed upon the tissues of the leaves, 

 taking out small amounts at different points. Very frequently 

 sufficient material is removed to cause the formation of small 

 holes which extend through the leaf. The diameters of these 

 holes are scarcely larger than that of a pin, yet a leaf is often 

 riddled to such an extent that its vitality is seriously affected. 

 In the plate the leaf affected with early blight shows the results 

 of the work of these insects, yet only the more serious part of the 

 injury could be represented. If a fresh leaf is closely examined 

 it will be found that there are many places in which the beetles 

 have begun to feed, yet when the epidermis of the leaf has been 

 penetrated, and only a few of the cells underneath have been de- 

 stroyed, the insect changed its base of operations, leaving scarcely 

 a trace to bear witness of its presence. It is true that often when 

 a leaf has been partially pierced, the color of the spot becomes 

 much lighter, but the intensity of the color depends very largely 

 upon the amount of injury done, and in certain cases the change 

 can scarcely be distinguished. 



The results of such repeated attacks of the flea-beetle cannot 

 be otherwise than disastrous to potato foliage, and I have heard 

 several growers maintain that the work of the flea-beetle is more 

 to be dreaded than that of any other organism which injures the 

 plants. In localities w^here these beetles are numerous, such 



