Effect of Copper Compounds 27 



all were heavier owing to the absorption of water. The pieces were 

 then immersed in pure water for another period of 24 hours, when 

 after drying and weighing, those from the weaker strengths of copper 

 sulphate ('001 '002) had absorbed yet more water, while those from 

 higher concentrations ('003 '004) had lost weight. So the author 

 assumes that for such pieces of potato the limit of toxicity lies between 

 '002 and "003 gm. mol. copper sulphate per litre. 



These experiments may possibly give some indication as to the 

 action of copper salts on plant roots. So long as the solution of copper 

 salt is dilute enough, the absorption layer of the root, acting as a semi- 

 permeable membrane and upheld by the resistant protoplasm, is able 

 to keep the copper out of the plant and to check its toxicity. As soon 

 as a certain limit is reached the copper exercises a corrosive influence 

 upon the outer layer of the root whereby its functions are impaired, so 

 that it is no longer able efficiently to resist the entry of the poison. 

 As the concentration increases it is easy to conceive that the harmful 

 action should extend to the protoplasm itself, so that the vital activities 

 of the plants are seriously interfered with and growth is entirely or 

 partially checked, death ensuing in the presence of sufficiently high 

 concentrations. 



2. Effect of copper on germination. 



The action of copper on the germination of seeds, spores and pollen 

 grains has attracted a certain amount of attention, and although the 

 results are apparently contradictory this is probably due to the different 

 plant organs with which the observers have worked. 



(a) Seeds. 



Miyajima (1897) showed that the germinating power of such seeds 

 as Vicia Faba, Pisum sativum, and Zea Mays was partly destroyed 

 by a 1 / solution of copper 1 , Zea Mays being the most resistant 

 and Vicia Faba the least resistant of the three. Micheels (1904-5) 

 stated that water distilled in a tinned copper vessel was more favourable 

 for germination than water from a non-tinned vessel. He suggests that 

 this is due to copper being present in the water in a colloidal form 

 in which the particles are exceedingly small and maintain themselves 

 in the liquid by reason of a uniform disengagement of energy in all 

 directions, to which energy the influence on germinating seeds must be 



1 The English translation in Just Bot. Jahresber. speaks only of a " solution of copper," 

 and in no case is the specific compound mentioned. 



