102 THE PEANUT— THE UNPREDICTABLE LEGUME 



reactions which are not entirely understood. Two other important ele- 

 ments, nitrogen and sulfur, often occur in the soil in the form of organic 

 matter and are released to the soil solution as a result of decomposition. 



The above discussion is only an indication of some of the factors in- 

 volved in supplying nutrients to the absorbing areas of plant roots. The 

 concentration of anions and cations of the soil solution is usually in- 

 creased by the addition of fertilizers, cover crops, lime and farm ma- 

 nures, as well as by nitrogen fixation by organisms and the removal of 

 sulfur and nitrogen from the atmosphere by rain water. 



The absorption and accumulation of ions by plant roots is a compli- 

 cated process involving internal factors such as transpiration, respiration, 

 photosynthesis and other metabolic activities associated with growth. 

 Aeration, moisture, temperature and other environmental conditions sur- 

 rounding the roots are also known to influence absorption. 



The absorption of ions by roots of the peanut plant is assumed to be no 

 different from that by other plants. However, since the fruit of the peanut 

 develops in the soil, its relation to ion absorption has been given con- 

 siderable attention. Several investigators (63, 68, 74, 88) suggested the 

 possibility of water and nutrient intake by the gynophore. Van der Volk 

 (85) observed that a soil extract aided fruit development, while Burk- 

 hart and Collins ( 19) were the first to demonstrate that an element, lith- 

 ium, was absorbed by the gynophore and distributed within the plant. 

 The latter workers also reported fruit quality to be benefited by the pres- 

 ence of calcium in the fruiting medium. Brady et al. (13, IS) demon- 

 strated that fruit filling was significantly increased when a single calcium 

 salt was added to the fruiting medium, while Harris (37) found fruit de- 

 velopment to be negligible when a calcium-deficient nutrient solution was 

 applied to that medium. It was reported {2i7) that yields were increased 

 when the sulfate ion was used in the fruiting medium, while Brady et al. 

 (15) failed to get a favorable response from that ion. It has been shown 

 also that nitrogen ^^* (84), phosphorus ^^*, and radioactive cobalt (37) 

 are absorbed in small quantities by the developing fruit and translocated 

 to other parts of the plant. Bledsoe et al. (9) found calcium*^* to be 

 actively absorbed by the shells and seed of developing fruit with some 

 s^^movement to other parts of the plant when the labeled calcium was ap- 

 plied to the fruiting medium. Conversely, when calcium *°* was applied 

 tolthe roots of the plant, a small quantity of the labeled calcium was 

 found in the shell, but never more than a trace could be detected in the 

 seed of developing fruit. 



* Small number refers to atomic weight. 



