190 HOW CROPS GROW. 



3. That the foliage and succulent portions of the plant 

 may include a considerable amount of sodium that is not 

 necessary to the plant ; that is, in other words, accidental. 



Can Sodium replace Potassium ? The close simi- 

 larity of potassium and sodium, and the variable quanti- 

 ties in which the latter especially is met with in plants, 

 have led to the assumption that one of these alkali-metals 

 can take the place of the other. 



Salm-Horstmar and Knop & Schreber first demon- 

 etrated that sodium cannot entirely take the place of 

 potassium that, in other words, potassium is indispen- 

 sable to plant life. Plate I, VI, shows the development 

 of buckwheat during 3 months, in Nobbe, Schroder & 

 Erdmann's water-cultures, when, in a normal nutritive 

 solution, potassium is substituted by sodium, as com- 

 pletely as is practicable. 



Cameron concluded, from a series of experiments which 

 it is unnecessary to describe, that, under natural condi- 

 tions, sodium may partially replace potassium. A partial 

 replacement of this kind would appear to be indicated 

 by many facts. Thus, Herapath has made two analyses 

 of asparagus, one of the wild, the other of the culti- 

 vated plant, both gathered in flower. The former was 

 rich in sodium, the latter almost destitute of this sub- 

 stance, but contained correspondingly more potassium. 

 Two analyses of the ash of the beet, one by Wolff (1), the 

 other by Way (2), exhibit similar differences : 



Asparagus. Field Beet. 



Wild. Cultivated. 1. 2. 



Potassium oxide 18.8 50.5 57.0 25.1 



Sodium oxide 16.2 trace 7.3 34.1 



Calcium oxide ...28.1 21.3 5.8 2.2 



Magnesium oxide 1.5 4.0 2.1 



Chlorine 16.5 8.3 4.9 34.8 



Sulphur trioxide 9.2 4.5 3.5 3.6 



Phosphorus pentoxide 12.8 12.4 12.9 1.9 



Silica 1.0 3.7 3.7 1.7 



These results go to show it being assumed that only a 

 very minute amount of sodium, if any, is absolutely nee- 



