60 Efect of Arsenic Compounds 



the plants turgescent in arsenic solutions for a bng time without 

 thereby increasing the toxic effect later on. The poisonous action 

 proceeds from the roots, of which the protoplasm is disorganised and 

 the osmotic action hindered. Finally, in the presence of sufficient of 

 the poison, the root dies without growth. 



Stoklasa (1896, 1898) again found that phanerogamic plants can 

 withstand arsenic poisoning for some time in the dark or in COj-free 

 air, provided that glucose is given in the food solution. The arsenic 

 poisoning is at its maximum during carbon assimilation by means of 

 chlorophyll. The toxic action of arsenious and arsenic acids, especially 

 in phanerogams, is due to injury to the chlorophyll activity. The 

 destruction of the living molecule is far more rapid in the chlorophyll 

 apparatus than in the protoplasm of the plant cell. 



Thus it seems that the physiological cause of the toxicity of arsenic 

 is partly a direct action on the root protoplasm, whereby its osmotic 

 action is hindered, and partly a detrimental action upon those func- 

 tions which are directly concerned with the elaboration processes of 

 nutrition. 



2. Effect of arsenic compounds on germination. 



In view of the great toxicity of arsenic to plants in their various 

 stages of development, one would naturally expect to find a similar 

 action with regard to the germination of the seeds. Davy (1859) 

 casually mentioned cases in which watering with arsenical solutions 

 or dipping seeds in arseniated water prevented germination. Heckel 

 (1875) found that arsenious acid checks germination and kills the 

 embryo at relatively feeble doses, '25 gm. to 90 gm. water^. Guthrie 

 and Helms (1903-4-5) carried out a systematic series of experiments 

 to test the effect of arsenic compounds upon different farm crops. 

 Various amounts of arsenious acid were added to soil in pot experi- 

 ments, and the seeds of the several crops were then sown. With barley, 

 wheat and rye O'lO/^ arsenious acid had little or no effect on germi- 

 nation, while an increase in the poison exercised a retarding action. 

 Maize could withstand 0'40 % arsenious acid without retardation being 

 perceptible. The aftergrowth with the different crops varied con- 

 siderably. The wheat plants with 0"10% arsenious acid grew all 

 right at first, but later on they developed weakly. The toxic action 

 increased rapidly as the strength of the poison rose in the different 



^ In the present state of our knowledge such a concentration seems relatively 

 strong I 



