Vedrödi (1893) tackled the problem at about the same time as Lehmann but from a rather different standpoint. He ratifies the statement as to the absorption of copper by plants, and going still further he states that in some cases the percentage of copper found in the seed may be four times as great as that occurring in the soil on which the plants grow, quoting one instance in which the soil contained ·051% CuO and the seed ·26% CuO. It is assumed that copper must play some physiological rôle in the plant, but no explanation of this action is yet forthcoming. Lehmann criticised Vedrödi’s figures of the copper content of certain plant ashes, and the latter replied in a further paper (1896) in which he brings most interesting facts to light. The quantity of copper in any species of plant varies with the individuals of that species, even when grown on the same soil, in the same year, and under similar conditions. The copper content of certain plants is put forward as a table, the years 1894 and 1895 being compared, and enormous differences are to be noticed in some cases. A quotation of the table will illustrate this more clearly than any amount of explanation. _Milligrams of copper in 1 kilog. dry matter._ 1894 1895 / \ / \ “Seeds” min. max. min. max. Winter wheat 80 710 200 680 Summer wheat 190 630 190 230 Maize 60 90 10 30 Barley 80 120 10 70 Oats 40 190 40 200 Buckwheat 160 640 150 160 “Fisolen” (Beans) 160 320 110 150 Linseed 120 150 110 150 Peas 60 100 60 110 Soy Beans 70 100 70 80 Lupins 80 190 70 290 Mustard seed 70 130 60 70 Paprika pods 790 1350 230 400 II. EFFECT OF COPPER ON THE GROWTH OF HIGHER PLANTS. 1. _Toxic effect._ (_a_) _Toxic action of copper compounds alone in water cultures._ The method of water cultures has been largely applied to determine the relation of copper compounds to plants. Twenty years ago (1893) Otto discovered the extreme sensitiveness of plants to this poison when grown under such conditions, as he found that growth was very soon checked in ordinary distilled water which on analysis proved to contain minute traces of copper. Controls grown in tap water gave far better plants, but this superiority was attributed partly to the minute traces of mineral salts in the tap water, and not only to the absence of the copper which occurred in the distilled water.