28 Effect of Copper Compounds 



attributed, the nature of the suspended substance determining whether 

 the influence be favourable or not. It is questionable, however, whether 

 Micheels was really dealing with a true colloidal solution of copper 

 or with a dilute solution of some copper salt produced by oxidation 

 of the copper vessel from which his distilled water was obtained. 



(6) Spores and pollen grains. 



Miani (1901) brought fresh ideas to bear upon the problem of the 

 action of copper on living plant cells, in that he sought to attribute 

 the toxic or stimulant effects to an oligodynamic action, i.e. spores 

 and pollen grains were grown in hanging drop cultures in pure glass 

 distilled water with the addition of certain salts or traces of certain 

 metals. While the salts are known to be often disadvantageous to 

 germination, Nageli had asserted that the latter often exerted an oligo- 

 dynamic action. In some cases pure copper was placed for varying times 

 in the water from which the hanging drop cultures were eventually 

 made, or tiny bits of copper were placed in the drop itself. Various 

 kinds of pollen grains were tested, and as a rule, pollen was only taken 

 from one anther in each experiment, though occasionally it was from 

 several anthers of the same flower. It was generally found that the 

 germination of pollen grains or Ustilago spores was not hindered by 

 the use of coppered water or by the presence of small bits of copper in 

 the culture solution. The only cases in which some spores or pollen 

 grains were more or less harmed were those in which the water had 

 stood over copper for more than two weeks, and even so the deleterious 

 effect was chiefly noticeable when the pollen itself was old or derived 

 from flowers in which the anther formation was nearly at an end. As 

 a rule germination was better in the presence of copper, whether in 

 pure water or food solution, the stimulus being indicated both by the 

 greater number of germinated grains and by the regular and rapid 

 growth of the pollen tubes. Miani attributes this favourable action to 

 the mere presence of the copper, corroborating Nageli's idea of an 

 oligodynamic action. 



3. Does copper stimulate higher plants? 



From the foregoing review it is evident that it is the toxic action 

 of copper that is most to the front, so far as the higher plants are 

 concerned, and that little or no evidence of its stimulative action 

 in great dilution has so far been discussed. Kanda dealt with this 

 question, with the deliberate intention of obtaining such evidence. 



