Other analyses of plants from zinc soils as against controls from normal soils indicated the high water and high ash content of the zinc plants, though the dry matter was low, and it is suggested that the increase of the ash may be connected with a stimulation caused by the zinc salts, unless it is due to phosphoric-acid hunger, since the calamine soils concerned are very deficient in phosphorus.
[Javillier (1908 c)] corroborated the early statements of Risse as to the presence of considerable quantities of zinc in certain species of Viola, Thlaspi and Armeria, and also he cited a list of other plants in which zinc occurs in some quantity. Javillier, however, is of opinion that zinc oxide, like the oxides of iron and manganese, is very common in plant ash, being present in all plant organs. Zinc is specially abundant in Coniferae, where it is probably characteristic, as is the presence of manganese in the ash and manno-cellulose in the wood. The so-called “calamine” plants show great powers of accommodation to large amounts of zinc.
[Klopsch (1908)] analysed 17 species of plants grown on soil in the vicinity of zinc works, and showed that the plants evidently absorb small quantities of zinc from their surroundings. He also regarded zinc as a normal constituent of certain plants.
II. Effect of Zinc on the Growth of Higher Plants.
1. Toxic effect.
(a) Toxic action of zinc salts alone in water cultures.
In comparison with copper little work has been done with regard to the action of soluble zinc salts alone on higher plants when grown in water cultures. [Freytag (1868)] stated that zinc salts must be very dilute if the plants are not to be harmed, and that for zinc sulphate the concentrations must not be more than 200 mg. per litre (= 1/5000). [Baumann (1885)] carried out further experiments and concluded that zinc salts are far more toxic than Freytag suspected, 44 mg. zinc sulphate per litre[5] killing plants of 13 species belonging to 7 families (Coniferae excepted). The various plants withstand the action of the zinc salts in different degrees, the same concentration killing off the species in different times. With the 44 mg. zinc sulphate the following results were obtained:—
| Trifolium pratense | killed in 16 days | ||
| Spergula arvensis | „ | 21 | „ |
| Hordeum vulgare | „ | 30 | „ |
| Vicia sativa | „ | 31 | „ |
| Polygonum Fagopyrum | „ | 60 | „ |
| Beta vulgaris | „ | 76 | „ |
| Onobrychis sativa | „ | 194 | „ |
With still less poison, 22 mg. zinc sulphate per litre, all the species mentioned were eventually killed with the exception of Onobrychis sativa, while 4·4 mg. zinc sulphate seemed to be harmless for all the plants tested except Raphanus sativus, which is evidently exceptionally sensitive to this toxic substance.
[Jensen (1907)] again indicated the poisonous action of zinc salts and also found that a relatively small reduction of toxicity was obtained by the addition of finely divided quartz to the solutions.