484 Trans. Acad. Sci. of St. Louis. 



the calcium compouud for the different algae used vary very 

 greatly from .3 to .1 N. In this consideration I have pur- 

 posely neglected the results obtained with magnesium iodide, 

 which might be omitted from the tables on account of the 

 fact that it was ascertained very soon after the experiments 

 were made that the magnesium iodide was wholly unstable 

 under the conditions, and the formation of hydroidic acid in 

 the solutions made the results more nearlj^ that for this acid 

 than for the nutrient salt with which the experiment began. 

 In this same table the chlorides of sodium and calcium are 

 not far apart, though there is ever}^ probability that the value 

 of the calcium compound was nearer .30 than .25, hence this 

 would be in keeping with the other results. 



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 * t and 

 others | § have found to hold in the nutrient relations of a 

 few fresh water algae and many phanerogams. Loew found 

 the magnesium salts esyjecially injurious to Spirogyra, and 

 his general conclusions indicate that he would exclude from 

 plants readily injured by the magnesium salts only certain 

 lower algae and the fungi. The marine algae which have 

 been used in my experiments represent undoubtedly what he 

 would class as higher algae, and their special relation to 

 magnesiuQi salts could only, from his standpoint, perhaps, be 

 explained as a special case, due to the peculiar conditions of 

 their normal environment. It should be borne in mind, how- 

 ever, that it would mean from the standpoint of his theory, 

 an ab-^ieuce of the hypothetical calcium protein compound in 



* Loew, O. The Physiological Role of Mineral Nutrients in Plants. Bui. 

 18. Div. Ve^. Plant Physiolo-.y said Palholosy, U. S. Dept. Agr., Washing- 

 ingtoQ. 1899. Bui. 45. Bureau of Plant Industry. 1903. 



t Loew, O. aud May, D. W. The Relation of Lime and Magnesia to 

 Plant Growth. Bui. No. 1. Bureau of Plant Industry, U. S. Dept. Agr. 

 1901. 



X Kearney, T. H., and Cameron, F. K. Some mutual Relations between 

 Alkaline Soils and Vegetation. Rept. No. 71. U. S. Dept. Agr. 1902. 



§ Loeb, J. Toxic and Antitoxic Effect of Ions, etc. Chap. 35. Studies 

 in General Physiology. Part II. 1905. Chicago. 



