120 



SPRAYING CROPS 



furnish easy access to the spores of disease-producing 

 organisms. 



Remedies — Spraying with arsenate of lead and 

 Bordeaux mixture will prevent to a great extent at 

 least the depredations of this pest. The more thorough 

 the application the more effective will it be. 



FUNGUS ENEMIES 



There are at least two distinct fungous diseases 

 which are called the Potato Rot or Potato Blight. 

 One of these is the Late Blight or Downy ]\Iildew, 

 due to the fungus Pliytopliora infestans; and the other 

 is the Early Blight or Leaf-spot Disease, due to 

 the fungus called Alteniaria sohni. They may usually 

 be distinguished by the fact that leaves aft'ected by 

 the former have on their under surface a white, velvety 

 mould, visible to the naked eye, but more readily seen 

 through the microscope ; with the Early Blight no such 

 mildew is present. \\\\\\ both, the foliage of plants 

 attacked becomes spotted with brown, and the spots 

 gradually enlarge, finally involving the whole leaf, 

 and then cause the stems to wilt and wither. 



According to Professor F. L. Scribner, the life- 

 history of the Downy ]\Iildew Potato Rot Fungus 

 may be summarized as follows : 'The spores lighting 

 upon the leaves of the potato germinate in drops of dew 

 or rain, and the product of germination — the zoospores 

 — penetrate to the interior tissues of the plant, and after 

 growing for a time through these tissues, the mycelium 

 sends out, chiefly from the under surface of the leaves, 

 slender fruiting branches, whereon are produced a new 

 crop of spores. These may carry the disease to the 

 other plants in the field, or to the other parts of the 

 same plant ; that is, they may serve to spread the dis- 

 ease in the tops, which we term blight, over the entire 

 field, or by being washed into the ground they may 



