176 HOW CROPS GROW. 



may include a considerable amount of soda that is not nec- 

 essary to the plant, that is, in other words, accidental.* 



Can Soda replace Potash ] The close similarity of pot- 

 nsh and soda, and the variable quantities in which the 

 latter especially is met with in plants, has led to the as- 

 sumption that one of these alkalies can take the place of 

 the other. 



Salm-Horstmar, and, more recently, Knop & Schreber, 

 have demonstrated that soda cannot entirely take the place 

 of potash in other words, potash is indispensable to plant 

 life. Cameron concludes from a series of experiments, 

 which it is unnecessary to describe, that soda can partially 

 replace potash. 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 cultivated plant, both 

 gathered in flower. The former was rich in soda, the lat- 

 ter almost destitute of- this substance, but contained cor- 

 respondingly more potash. Two analyses of the ash of 

 the beet, one by Wolff, (1.,) the other by Way, (2.,) ex- 

 hibit similar differences : 



Asparagus. Field Beet. 



Wild. Cultivated. 1. 2. 



Potash 18.8 50.5 57.0 25.1 



Soda 16.2 trace 7.3 34.1 



Lime 28.1 21.3 5.8 2.2 



Magnesia 1.5 4.0 2.1 



Chlorine 16.5 8.3 4.9 34.8 



Sulphuric acid 9.2 4.5 3.5 3.6 



Phosphoric acid 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 soda, if any, is absolutely neces- 

 sary to plant-life that the soda which appears to replace 

 potash is accidental, and that the replaced potash is acci- 



* Soda appears to be essential to animal life ; since all the food of animals is 

 derived, indirectly at least, from the vegetable kingdom, it is a wise provision 

 that soda is contained in, if it be not indispensable to plants. 



