190 HOW OBOPS GfiOW. 



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 alkaliTmetals 

 can take the place of the other. 



Salm-Hovstmar and Knop & Schreber fir:t demon- 

 strated 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 & 

 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 m'dj 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 [H), exhibit similar differences : 



• ' Asparagus. Field Beet. 



Wild. Cultivated. 1. 2. 



Potassium oxide 18.8 50.5 67.0 25.1 



Sodiiim oxide 16.2 trace 7.3 34.1 



Caloiiim 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 



Siilphur trloxide 9.2 4.5 3.5 3.6 



Pliosphorus 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- 



