302 JAMES GEERE DICKSON 
Boehm (1875) was perhaps the first to call attention to some of 
the specific actions of magnesium salts in culture solutions, and much 
recent work has demonstrated the toxic action, at least upon green 
plants, of magnesium salts either alone or when present in excess of a 
certain ratio to the other bases. It has been shown that magnesium 
is required for the proper growth of fungi and that, contrary to what 
occurs in the case of green plants, magnesium may be present in very 
large quantities without causing a toxic effect. These results have 
been confirmed by the unpublished work of Mr. J. P. Bennett in this 
laboratory. This relation of magnesium is in part explained by the 
fact that magnesium neutralizes the organic acids formed in certain 
metabolic processes of the fungi and is thus taken out of the field of 
action. Loew (1892), Bokorny (1895), and Reed (1906) have sug- 
gested that magnesium plays an important part in the assimilation 
of phosphorus and phosphoric acid. It has been found by Sullivan 
(1905) that certain bacteria can form lipochromes in normal quantity 
only in the presence of magnesium sulphate and of a phosphate. 
Others have demonstrated the intimate relation between the presence 
of magnesium and the formation of vegetable oils, which probably 
accounts for the high magnesium content of many seeds. Aso (1901) 
had previously shown by analyses that spores of Aspergillus oryzae, 
which contain a large amount of fat, contain also a moderately ^arge 
proportion of magnesium. 
Nobbe (1870) first pointed out that carbohydrates are formed 
normally only in the presence of potassium, and Loew (1880) suggested 
that potassium plays an important role in promoting the chemical 
condensation of proteins, carbohydrates, and fats in plant synthetic 
processes. Loew's idea is partly based upon Nageli's (1879) assertion 
that the potassium salts are better adapted to catalytic work than 
sodium vsalts, because of their generally greater affinity for water. 
It was shown by Schimper (1890) that potassium is essential to the 
normal development of growing apices. Breazeale (1906) found that 
plants previously grown in solutions lacking potassium or sodium 
absorb large quantities of potassium when tiansferred to a normal 
nutrient solution containing both these elements. 
Early investigations demonstrated that phosphorus is necessary 
for plant growth and that it occurs chemically combined with many 
plant substances. Harden (191 1) suggested the necessity of phos- 
phorus in fermentation and other enzymatic activities. 
