32 



PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



ethereal extract of the "potassium plants" was of a normal pure green, 

 while that of the "rubidium plants" was of a yellowish green; (2) that 

 the rubidium plants contained 7.8 per cent of glucose in the dry mat- 

 ter, while the potassium plants contained none; (3) that there was 

 more starch in the potassium plants than in the rubidium plants. 



The writer has observed further that the replacement of even one- 

 half of the potassium chlorid in a culture solution by rubidium chlorid 

 will impede the development, the plants reaching after six weeks only 

 half the size of the control plants. Moreover, the leaves were partially 

 rolled in, the flowers were scanty, and the plants died before the seeds 

 ripened. 



These experiments proved that it is impossible to raise normal seed- 

 bearing' buckwheat plants when the chlorid of potassium in the culture 

 solution is replaced by chlorid of rubidium, but on the other hand they 

 left hardly any doubt that rubidium chlorid can serve for certain 

 physiological functions of which sodium chlorid is utterly incapable. 

 With rubidium chlorid, buckwheat plants may reach a dry weight of 

 even thirty- three times that of the seeds, but with sodium chlorid they 

 seldom reach over five times. In a normally raised plant, however, 

 the dry matter may be over six hundred times the weight of the seed. 

 In the experiment with rubidium chlorid starch was formed b} r assimi- 

 lation, but in those with sodium chlorid none was formed. The flower- 

 ing* stage was reached in the former case, but not in the latter. With 

 rubidium chlorid pathologic phenomena made their appearance chiefly 

 after the flowering stage, but with sodium chlorid starvation phe- 

 nomena were observed very much earlier. 



Recent experiments of the writer have proved that rubidium chlorid 

 exerts a powerful stimulating action on the growth of plants when 

 added in doses of 10 to 200 milligrams to 1 kilo of soil in which all 

 mineral nutrients are present. Ten milligrams sufficed to show this 

 effect with Brassica chinensis, while 200 milligrams had a surprising- 

 effect with barley. A loamy soil was manured per kilo with 1.5 

 grams ammonium sulphate, 0.5 gram sodium nitrate, 1.5 grams cal- 

 cium superphosphate, 0.5 gram monopotassium phosphate, and 1 

 gram potassium carbonate. In the one case were added 200 milli- 

 grams rubidium chlorid; in the other an equivalent amount of sodium, 

 chlorid (control case). Fife barle}^ plants, cut soon after the flowering 

 stage, yielded the following result, the rubidium plants being normal 

 in every regard: 



Result of experiments with Fife barley plants. 



Part of plant. 



I Ears (fresh weight) 



Living leaves and stalks (fresh) 

 Dead leaves (air dry) 



Rubidium 



plants. 



Control 

 plants. 



Grams. 



Grams. 



6.1 



3.7 



87.3 



53.6 



5.2 



4.8 



