28 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



Potassium or sodium iodid. even in small doses, exerts a poisonous 

 influence on animals as well as on plants. Germinating buckwheat 

 seeds placed in a full mineral solution in which the potassium was 

 offered as iodid, died before the first leaf was developed, as the writer 

 observed many years ago. The poisonous action of the iodid of potas- 

 sium is no doubt due to the liberation of iodin by oxidation favored 

 hj the acid cell sap. Lower organisms without acid juices are rather 

 indifferent in this respect. The writer found certain algae and infu- 

 soria alive in culture water live weeks after 0.5 per cent of iodid of 

 potassium had been added to it. On the- other hand. 0.2 per cent 

 potassium iodid killed larger kinds of Spirogyra within a few days 

 when the culture solution contained traces of the acid monopotassium 

 phosphate. Lower fungi and bacteria are not injured in neutral cul- 

 ture solutions to which even 1 per cent of this iodid is added. Potas- 

 sium iodid has been found by bacteriologists to possess a germicidal 

 action only when present in large doses. In very small doses of 25 to 

 300 grams per hectare iodids stimulate growth and increase the harvest. 



THE PHYSIOLOGICAL ROLE OF ALKALI SALTS. 



IMPORTANCE OF POTASSIUM FOR THE FORMATION OF STARCH AND 



PROTEIN. 



The paramount importance of potassium salts for every living cell is 

 firmly established. In green plants they are concerned not only in the 

 synthesis of carbohydrates, but also in that of the protein bodies, since 

 not only is there an increase of potassium salts in such parts of green 

 plants as are developing rapidly and consequently forming large 

 amounts of protein, but most fungi, even in the presence of such a 

 favorable nutrient as sugar, are found to require potassium salts for 

 the production of protein. These salts can never be replaced by 

 lithium a or sodium salts, but in certain fungi they may be replaced to 

 a limited extent by rubidium or caesium salts. 



It is a well-known fact that plants cultivated in the presence of more 

 sodium than potassium salts will nevertheless absorb a greater quan- 

 tity of the latter than of the former. The amount of potash annually 

 required per hectare of pine forest is about 7.5 kilos, of wheat field 

 37.5 kilos, of clover field 10:2 kilos, and of potato field 125 kilos. 

 Other things being equal, an increase of potash will increase to a cer- 

 tain degree the percentage of carbohydrates, e. g., starch and sugar, 

 and. further, potash is reported to be present in larger proportions in 

 those parts in which the carbohydrates are transported, as in the 

 parenchyma of the bark and pith. 



(' Although lithium gaits exert a noxious action on phanerogams they do not 

 readily affect alga?. Spirogyra still appeared normal after four weeks in a complete 

 culture solution to which 0.3 per mille lithium chlorid was added. At a higher con- 

 centration, however, the result may be different. 



