176 HOW CEOPS GEOW. 



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- 

 ash 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 e^^iVeZy 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 partialis/ 

 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 alftilyses of the ash of 

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

 hibit similar differences : 



Axparagtis. Field Beet. 



Tl'iU. CuU iijated. 1. 3. 



Potasli 18.8 50.5 57.0 2S.1 



Soda 16.3 trace 7.3 34.1 



Lime 28.1 31.3 5.8 3.3 



Magnesia 1.5 4.0 3.1 



Chloriue '....16.5 8.3 4.9 34.8 



Sulphuric acid 9.3 4.5 3.5 3.6 



Phiosplioric acid 13.8 13.4 13.9 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 Boda is contained in, if it be not indispensable to plants. 



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