Hoagland — 166 — P lant Nutrition 



cause of interionic competition. The absence of nitrate 

 is also to be considered since the absorption of potas- 

 sium tends to be accelerated by the absorption of a 

 mobile anion like nitrate. 



The quantitative relations among basic ions ab- 

 sorbed: namely, potassium, calcium, magnesium and 

 sodium are of considerable physiological importance. 

 It is not unusual to find that the decrease in absorption 

 of one base will be compensated roughly by an increase 

 in absorption of other bases, so that the total equiv- 

 alents of bases present in the plant tissues will remain 

 approximately constant. But this does not always 

 occur. The decreased absorption of potassium will 

 not necessarily be fully compensated by the increased 

 absorption of other bases. Many types of plants ab- 

 sorb potassium much more readily than calcium or 

 magnesium, although the impression should not be 

 held that potassium ions are always more mobile in 

 absorption than calcium, magnesium or sodium ions. 

 The work of Collander illustrates that the genetic 

 characteristics of the plant as well as the physical- 

 chemical characteristics of the ions determine the 

 relative amounts of different ions absorbed from solu- 

 tions containing equivalent concentrations of the sev- 

 eral bases. Certain leguminous plants, for example, 

 absorb calcium about as readily as potassium. So do 

 some non-leguminous species.* 



Leaving aside the cases in which calcium, in terms 

 of equivalents, can gain entrance into the plant at a 

 rate comparable with that for the entrance of potas- 

 sium, a general survey of knowledge of plant nutrition 

 leads to the conclusion that for most types of higher 

 plants for which evidence is available, the building 



*Often the question presents itself, of how the amounts 

 of nutrients absorbed should be computed, whether as total 

 amounts per unit number of plants, or per unit mass of soil, 

 or as percentage of tissue produced by the plant. The former 

 method is required for some purposes, but the latter is probably 

 more enlightening in discussing the problems now under con- 

 sideration. 



