PLANT METABOLISM 



409 



Reproduced from Hiinfjer .S'l'.r/ns in Crops, a publication of tlie American Society 

 of Agronomy and tlie National Fertilizer Association, Washington, D. C. 



Fig. 15-9. Tobacco plants suffering from various mineral deficiencies — 

 B, nitrogen; C, phosphorus; D, potassium; E, boron; F, calcium; G, 

 magnesium. Reduction of growth has occurred in all cases. A is a normal 

 plant. 



of the general function of mineral elements in Chap. 8, animals require 

 all of these elements except boron. 



The cells of the root have a capacity for selective intake of ions. For 

 example, from a solution high in sodium and low in potassium, the plant 

 may absorb much more potassium than sodium. From soil the plant 

 obtains its cations, such as Ca + + , by base exchange (that is, by a 

 process by which the plant exchanges metabolic hydrogen ions for a 

 cation adsorbed on a soil colloid). In contrast, the plant absorbs its 

 anions, such as SO4"", from the soil solution around the roots. 



Some effects of certain mineral deficiencies are illustrated in Figs. 

 15-9 and 15-10. 



