508 Reed . — The Value of Certain Nutritive Elements 
4. Previous work on the role of magnesium. 
Boehm (’75) seems to have been almost the first one to point out any 
specific action of magnesium salts upon plants. It was quite natural that 
he should have discovered the toxic action of magnesium salts in solutions 
when he attempted to use these salts in water cultures. Von Raumer (’83) 
went further and pointed out the antidoting power of calcium for mag- 
nesium, and the ratio of the two elements necessary for the best growth of 
plants. He observed that Phaseolus plants suffered characteristic injury 
when grown in the absence of magnesium. After becoming about one 
meter high the internodes of the plants ceased to elongate, and the new 
leaves remained small and chlorotic. 
The apparent toxic qualities of magnesium salts have already been 
mentioned in discussing the action of calcium salts, but other considerations 
necessarily come up at this place. Loew holds the view, previously 
mentioned, that magnesium salts cause injury as a result of displacing 
the calcium ions from certain important proteid compounds, and that the 
resulting magnesium compound is not capable of performing the normal 
functions necessary to the continued existence of the living tissues. 
According to his view a proper ratio of calcium and magnesium salts 
should be afforded, if the normal processes of the cell are to continue. 
In this regard the recent paper by Duggar (’ 06 ) is of value. In 
a careful study of the toxic action of various salts added to sea water, he 
found that magnesium salts had a very low toxicity for marine algae. 
Granting, as we must, in the light of our present knowledge, that the 
marine algae are able to withstand much greater concentrations of mag- 
nesium salts than fresh water algae, or phanerogams, it is difficult to see 
how this great group of plants (some of them possessing a truly high 
organization) conforms to the general statements made by Loew, concerning 
the replacement of calcium by magnesium in the hypothetical calcium- 
proteid compound. Duggar found that ammonium salts had a greater 
toxic effect than any other basic radical which is ordinarily regarded as 
a nutrient for an autotrophic plant. Arranged in the order of their toxicity 
for marine algae, his paper gives the series NH 4 , K, Ca, Mg. He states 
further, ‘The very low toxic effect of the neutral magnesium salts upon 
the marine algae makes it evident that these plants are very notable 
exceptions to the rule which Loew and others have found to hold in the 
nutrient relations of a few fresh water algae and many phanerogams.’ The 
great preponderance of magnesium over calcium in the experiments made 
by Duggar shows that the protoplasm of these plants is not seriously 
injured by magnesium. 1 
1 Loew has suggested that such plants are able to withstand large amounts of magnesium on 
account of the acidity of the cell sap. It is difficult to see how the acidity of the cell sap can 
