25 Gisiger: Deficiencies Caused by Excesses 



of calcium compounds will cause injuries in the root zone of the plants. 

 6) Boron has been employed with success for a long time against the 

 damage by alkaline reaction but a certain amount of leaching also gives 

 good resvdts. In a humid climate, leaching can be effected by drainage 

 and lowering of the water table. 



The antagonism between boron and hydroxide COH^-ions.— 

 In accordance with certain statements in the Hterature, I beheve 

 that the results obtained here confirm once more the fact, that 

 "lime injury" in plant growth is traceable to a high concentration 

 of OH-ions in the soil. The liming causes a part of these injuries 

 indirectly; these injuries are never a direct result of the concen- 

 tration of calcium ions in the soil. 



According to Pallmann, the hydroxide (OH) -group is 

 among the hydrophile radicals which favour hydration. We may 

 well assume an extreme hydration (swelling) of the root tips in a 

 strongly alkaline soil. The root tips are also exposed to the micro- 

 organisms by which they can be decomposed. As the osmotic 

 pressure of the roots is reduced they are unable to penetrate into 

 the soil which is oversaturated with hydroxide ions. On the 

 other hand, when such penetration still occurs their reduced os- 

 motic pressure makes the absorption of water difficult (Schropp 

 and Arenz). 



In contrast to the hydroxide ions, boron has dehydrating prop- 

 erties; according to Noack it can withdraw water from swelled 

 gelatine. Similar observations were made by Schmucker with 

 germinating pollen. Pollen hydrates in a nutritive solution so 

 strongly without boron that the germinating tube bursts, whereas 

 the tube remains intact when boron is added. These facts offer 

 an acceptable explanation of the harmful effect of the hydroxide- 

 ions without the hypothesis of a higher boron fixation by lime. 



In acid soils, overliming results in too great a concentration of 

 OH-ions which cause the roots to swell too much. To prevent 

 this, the roots must be able to assimilate an adequate supply of 

 boron. The physiological balance has to be restored by a high 

 boron dressing to provide for a strong assimilation of the element. 

 In this case the boron does not act as a nutrient in the usual way 

 but rather as a medicine. The higher doses of boron strengthen 

 the plant roots against the unfavourable and harmful influence of 

 the OH-ions. This hypothesis or theory avoids the conflicting 

 views expressed in the earlier theory according to which the dam- 

 age was ascribed to the Ca-ions and also to a fixation of boron by 

 them. 



