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, Nägeli had asserted that the latter often exerted an oligodynamic 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 Nägeli’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, if it existed. He worked with _Pisum sativum_, var. _arvense_, _Pisum arvense_, _Vicia Faba_, var. _equine_ Pers, and _Fagopyrum esculentum_ Mönch, which were grown in glass distilled water, without any food salts, so that the plants were forced to live on the reserves in the seeds, which were carefully graded to ensure uniformity of size. It was found that in water cultures copper sulphate solutions down to ·00000249% (about 1 in 40,160,000) are harmful to peas, and still further down to ·0000000249% (about 1 in 4,016,000,000) the copper salts act as a poison rather than as a stimulant. Against this, however, is the statement that in certain soils copper sulphate acts as a stimulant when it is added in solution. Jensen again could obtain no stimulation with copper sulphate.