2 4 o PLANT AND ORGANIC CHEMISTRY 
of their fixed ingredients.” 1 If an ash-constituent can pass 
through a cell wall, its absorption will take place independently 
of its use or harmfulness to the plant, but the absorption of es¬ 
sential inorganic constituents will depend upon its relation to 
the metabolism of the plant. 
The ash-constituents of a plant increase from the roots up¬ 
wards to the leaves, a fact showing that the leaves are the organs 
in which more especially active chemical changes take place. 
The ash ingredients are usually present in each plant cell; in 
the cell wall, imbedded in the cellulose, and partly in the con¬ 
tents of the cell. The salts of the alkaline metals and of the sul¬ 
phates and the chlorides of magnesium and calcium occur in 
the solution of the sap. Silica and phosphates of calcium and 
magnesium are mostly insoluble and exist in the tissues of the 
plant. 
Water-culture experiments 2 have shown the essential ash- 
ingredients. Potassium, like phosphorus, is always found in 
relation with living protoplasm. If 3 the plant was not supplied 
with potassium, it grew very little, and very little starch was 
formed in the chlorophyll corpuscles of the leaves. On the addi¬ 
tion of potassium chloride, the starch grains became more nu¬ 
merous in the leaves, and made their appearance in other parts 
of the plants. Potassium, doubtless, plays an important role 
in the formation and the storing up of carbohydrates, for the 
organs in which these processes are active, as the leaves, seeds, 
and tubers, are found to be the richest in this element. 
It has been observed that caesium 4 and rubidium can replace 
potassium in the food of certain fungi (mould, yeast, and bac¬ 
teria). 
Salm-Horstmar describes 5 some experiments, from which 
he infers that minute traces of lithium and fluorine are indis¬ 
pensable to the fruiting of barley. The same investigator has 
concluded that a trace of titanic acid is a necessary ingredient 
of plants. 
1 How Crops Grow , by S. W. Johnson, London, p. 145. 
2 Nobbe, Siegelt, Wolff, Stohmann, Sachs, and others. 
3 Nobbe, Die organische Leistung des Kaliums., 1871. 
4 Naegeli, Sitzber. d. Akad. d. Wiss . zu München , 1880. 
5 Jour, für Prakt. Chem 1884, p. 140. 
