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- 
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 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. oe 
Wild. Cultivated. 2. 
POtASH sis siawincseeeienes 18.8 50.5 57.0 25.1 
BOG ccc casas cece eee 16.2 trace 7.3 34,1 
DME se ciel Sse enewte 28.1 21.3 5.8 2.2 
Magnesia............. L5 — 4.0 21 
CMI occ s bata coe ee 16.5 8.3 4.9 84.8 
Sulphuric acid......... 9.2 4.5 8.5 3.6 
Phosphoric acid....... 12.8 12.4 12.9 1.9 
Bienes oie sicie vecie sigsersig eee 1.0 3.7 3.7 17 
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, indircctly at least, from the vegetable kingdom, it is a wise provision 
that soda is contained in, if it be not indispensable to plants. 
