26 Effect of Copper Compounds 



are capable of solution by the cell-sap. Salts of arsenic, copper, lead, 

 zinc and mercury were intimately mixed with soil, 30 grams of the 

 poison being added to 307 cubic decimetres of soil, two plants separated 

 by a partition being grown on this quantity. The test plants were 

 Polygonum Fagopyrum, Pisum sativum, Secede cereale and Panicum 

 italicum, and all the plants developed strongly and normally except the 

 last named. The Panicum developed very badly coloured leaves in 

 an arsenic-containing soil, and the plants were killed soon after they 

 started in soils containing copper. After harvesting, the crops were 

 analysed and no trace of copper was found in any one of the experi- 

 mental plants by the methods adopted. Also the absorption capacity of 

 different soils for different poisons was shown to vary, for basic salts are 

 absorbed, while acids may pass completely through the soil into the 

 drainage water. 



These results obtained by Gorup-Besanez are possibly not altogether 

 above criticism, for later workers showed that copper was absorbed to 

 some extent by plants grown in water cultures, and if that is so it seems 

 unlikely that no absorption should take place from soil. Nevertheless, 

 the absorption is very slight, for apparently living protoplasm is very 

 resistant to copper osmotically. Otto showed that beans, maize and 

 peas can have their roots for a long time in a relatively concentrated 

 solution of copper sulphate, and yet take up very little copper indeed, 

 but analyses do reveal slight traces after a sufficient interval of time 

 of contact has elapsed. Berlese and Sostegni indicate that the roots of 

 plants grown in water culture in the presence of bicarbonate of copper 

 showed traces of copper. 



Verschaffelt (1905) devised an ingenious method of estimating the 

 toxic limits of plant poisons, though it is rather difficult to see how 

 the method can be put to practical use with water culture and soil 

 experiments. Living tissues increase in weight when put into water 

 on account of the absorption of water. Dead tissues do not, as 

 they have lost their semi-permeable characteristics, so a decrease in 

 weight takes place owing to part of the water passing out. This 

 principle is applied by Verschaffelt to determine the " mortal limit " 

 of external agents in their action on plant tissues. Root of beetroot, 

 potato tuber, aloe leaves, and parts of other plants rich in sugar all 

 came under review. The parts were cut into small pieces weighing 

 about 3 5 grams, dried with filter paper, weighed, and plunged into 

 solutions of copper sulphate of varying strengths from '001 "004 gm. 

 mol. per litre, and left for 24 hours. After drying and again weighing 



