The effect of light upon plant growth is a problem which has attracted many workers since the discovery of Priestly, in 1771, that a plant could purify fixed air, carbon dioxide, which was followed by the supplementary work of Ingen-Housz and Senebier, who showed that the phenomenon was associated with the nourishment of the plant, and took place only in sunlight and through the agency of the green portions of the plant.
Various attempts have been made to substitute certain elements for those acknowledged as essential for plant growth. Using plant material, sodium is the element usually chosen as a possible substitute for potassium, but results show that whilst sodium may be taken up in fairly considerable quantities this is only possible if small amounts of potassium be present as well. Total replacement appears to be impossible (11,13,15).
1. The results are given of the poisoning of Nitocra spinipes (Boeck) by copper and mercury salts used together and separately.
2. The state of copper and mercuric salts in sea water is examined using the available physico-chemical data.
3. The results suggest that the two poisons act in a different manner and possible reasons for this are considered.
4. The striking synergic effects obtained when the two metals are used together are considered to support the suggestion in 3 above and various possible explanations, both biological and chemical for this synergism, are examined.
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