24 



Since the properties of elements are to a certain extent functions of 

 tlieir atomic weight, it might be sui)posecl that the ^physiological capa- 

 bihties of the alkali metals would increase with their atomic weight, 

 but the facts observed are not in accord with this view. Birner and 

 Lukanus ^ demonstrated that plants soon perish when the culture solu- 

 tions contain rubidium or caesium nitrate in place of potassium nitrate. 

 In experiments with buckwheat plants the writer afterwards confirmed 

 this conclusion as regards rubidium nitrate,- not taking CcTsium salts 

 into consideration ; but he observed in addition that the action of rubid- 

 ium chlorid differed to some extent from that caused by rubidium 

 nitrate. Where the chlorid was offered the plants attained a greater 

 height than with the nitrate. Those with rubidium nitrate died before 

 the flowers were formed, while those with rubidium chlorid died after 

 that period. Torsion and thickening of the stalk and curling and 

 rolling up of the leaves were the most striking results with rubidium 

 nitrate. In both cases, however, a diagnosis of the pathologic char- 

 acters revealed essentially a disturbance in the functions of the chlo- 

 rophyll bodies and in the transportation of starch, the effect on the 

 latter being more marked with the nitrate than with the chlorid. A 

 chemical comparison of buckwheat jDlants grown with potassium 

 chlorid and of those grown with rubidium chlorid showed (1) that the 

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

 while that of the "rubidium plants" was of a yellowish green j (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 phy- 

 siological 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 mat- 

 ter may be over six hundred times the weight of the seed. In the experi- 

 ment with rubidium chlorid starch was formed by assimilation, but in 

 those with sodium chlorid none was formed. The flowering stage was 



iLandw. Vers. Stat., Vol. VII, p. 363. 

 = Ibid., Vol. XXI, p. 389. 



^A certain writer's recent statement that rubidium salts have a poisonous effect 

 on plants has to be somewhat modihed. 



