THK POTATO 



FIG. 34 SECTION OF A POTATO LEAF 

 (After Marshall Ward) 



Showing the parts and the threads, or mycelium, of the blight or rot (Phy- 

 tophthora infestans). a Epidermis, or outer cells, b Palisade cells, which 

 aid in giving rigidity and firmness to the leaf, and in the manufacture of 

 starch and other ingredients, c Spongy tissue, showing cells and large 

 air spaces between, d The stomata, or breathing pores of the leaf, with 

 aerial branches of the parasite growing outward through them, e The 

 spore sacs, or conidia, in which the spores, or seeds, are formed, f A pe- 

 culiar hair on the under surface of the leaf. The dots in the cells are the 

 chlorophyll granules, which give the green color to the leaf, and aid in the 

 production of starch. The dark parts of the tissue show where cells are 

 dying from the effects of the disease. I,oss of cells means a reduction in 

 the amount of food prepared, and, consequently, reduced yield. In New 

 York alone the farmers lose $8,000,000 to $10,000,000 annually from diseases, 

 and because they do not spray. This is the most important disease preva- 

 lent at present. 



Aids to Attack. i. Flea-beetles puncture the leaves 

 and furnish easy access for the spores to the inner 

 parts of the leaf. 



2. Humid, still days, with a tempera4ure of about 73 



