As soon as the presence of zinc in members of the vegetable kingdom was established the question arose as to its effect upon both the plant and the soil. Gorup-Besanez (1863) grew plants in soil with which 30 grams of metallic poisons such as CuSO₄, ZnSO₄, HgO, were intimately mixed with 30·7 litres (“cubik Decimeter”) of soil[6]. On analysing the ash of _Secale cereale_, _Polygonum Fagopyrum_, and _Pisum sativum_ after six months growth he failed to detect the presence of zinc in any one of the three. As the results varied with different poisons on different plants he concluded that the absorption capacity of the various kinds of soils for different poisons varies, that basic salts are absorbed, while the acid salts may pass completely through the soil in the drainage water. [6] This is equivalent to about ·1% of poison. Freytag (1868) stated that zinc is retained by the soil in the form of oxide, which is derived from dilute zinc compounds as they filter through the soil, by decomposition by the salts of the soil. For field earth the limit of absorption of zinc oxide from zinc sulphate is between ·21%–·24% of the earth. F. C. Phillips (1882) corroborated Freytag’s statement as to the absorption of small quantities of zinc by the roots of plants, but he states as a fact that both lead and zinc may enter plant tissues without causing any disturbance in the growth, nutrition or functions of the plants, a conclusion that is obviously incorrect or at least incomplete in view of later work on the subject. His choice of plants was certainly unusual, including geraniums, coleas, ageratums and pansies, the poison used being zinc carbonate. Holdefleiss (1883) stated that in spite of a soil content of 2% zinc the vegetation was not in any way harmed, clover fields and meadow lands on zinc soil presenting a normal appearance. This observation was quite inconclusive, as the author proceeds to say that of the plants that were able to absorb zinc salts without disadvantage the most luxuriant were the so-called zinc plants--the exceptions that prove the rule. Two years later Baumann showed that such insoluble zinc salts as the carbonate and sulphide in the soil cannot hurt plants. These salts are certainly dissolved to some extent by water containing CO₂ but solution is hindered by the constitution of the soil. He also found that the various kinds of soil act differently upon zinc solutions, the absorptive power of pure humus soils (“reinem Humusboden”) for zinc solutions being the strongest. Clay and chalk soils also decompose such solutions energetically, while poor sandy soils have only a weak power of absorption. This selectivity of absorption may account for the difference in the toxicity of zinc salts to plants in the various soils.