190 HOW OBOPS GEOW. 



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 fir:t demon- 

 strated that sodiam 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 & 

 Erdmanu'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 maj 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 : 



Asparar/us. Field Beet. 



Wild. Cultivated. 1. 2. 



Potassiiun oxide 18.8 60.5 67.0 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 



CMorlne .*. 16.5 8.3 4.9 34.8 



Sulphur trloxlde 9.2 4.5 3.5 3.6 



Phosphorus pentoxlde 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- 



