Nature of Plant Diseases 



97 



about by lack of, or by an excess of, certain food 

 elements in the soil. The effect is an interference 

 with the proper life functions of plants. 



Malnutrition 



Symptoms. The symptoms of malnutrition are 

 not always the same. They differ somewhat with 

 the crop, the nature of the soil, and the fertilizer 

 applied. In malnutrition the symptoms to be looked 

 for are retarded growth, change of color in the foli- 

 age and root injury. Affected plants remain 

 dwarfed at a time when maximum growth is ex- 

 pected. The color of the foliage turns a lighter 

 green, especially in the spaces between the veins, 

 which become yellowish green to brown. Roots of 

 such plants are poorly developed, and secondary 

 roots are often missing. 



Causes of Malnutrition. The work of Stone*, 

 and Harter f and others seems to have established 

 the fact that malnutrition cannot be attributed to 

 the work of parasitic organisms. Stone cites in- 

 stances where constant watering with liquid fertil- 

 izers or manure would cause malnutrition in cucum- 

 ber plants. The same is also induced when pig and 

 cow manure are mixed, or when manure is worked 

 into a soil already well fertilized otherwise. Harter 

 records cases of malnutrition brought about by an 



♦Stone, G. E., Massachusetts Agr. Expt. Sta., Ann. Rept., 5-13: 

 X910. 



t Harter, L. L., Virginia Truck Expt. Sta., Bui. i: 4-16, 1909 

 (Norfolk, Va.). 



