ii6 



THE POTATO 



ture. The degree of immunity 

 varies with our ability to keep 

 the whole of the plant covered 

 with an armor of Bordeaux 

 mixture. Plants half sprayed 

 are not secure, as the disease 

 can spread rapidly inside the 

 plant. The plant must be com- 

 pletely coated all the time to be 

 immune. This may be impos- 

 sible when a plant is growing, 

 but this is not the fault of the 

 Bordeaux mixture. The more 

 thoroughly and more frequently 

 the spraying is done the better 

 the chances of bringing the 

 crop through. It will be seen 

 that Bordeaux is but a prevent- 

 ive; it is not a cure. Hence, 

 the poor results from spraying 

 after the disease has obtained a 

 foothold. 



2. Obtaining disease-resisting 

 varieties, or changing the seed 

 if it has lost its resisting power. 



3. Planting on fresh ground, 

 and planting early. 



4. Giving good cultivation, 

 and having a good rotation. 



5. Destroying all refuse of 

 potatoes. 



6. Having good drainage — both water and air drain 



FIG. 36 — LONGITUDINAL 

 SECTION OF A POTATO 

 STALK, SHOWING A GER- 

 MINATING STORE OF ROT 



{Phytophthora infestans) 

 (After Marshall Ward) 



The number of stomata per 

 square inch on a potato stem 

 is much smaller than in the 

 case of a leaf, but here the 

 germ tube has pierced the 

 cell wall, and is growing in 

 the cell. In spraying, the 

 stems should be coated with 

 Bordeaux. 



