THE ACTION OF ARSENIC ON LEAVES

¹ From the Laboratory of Plant Physiology of the Henry Shaw School of Botany at Washington University, Saint Louis, Missouri

1. The leaves on living plants dipped in arsenic solution of lethal strength and afterwards washed out with water retain for a while their living capacities (plasmolysis and evaporation). The death of these leaves takes place gradually.

2. The dipping of leaves of a living plant in a toxic solution of arsenic has the following action on their water metabolism: the leaves continue to evaporate the water like normal leaves when cut off and not dipped in arsenic. The leaves on plants after having been dipped in arsenic solutions lose the same amount of water per square centimeter of the surface and per unit of time as normal leaves, when cut off, but the leaves dipped in arsenic lose the capacity to get the water from the plant.

3. The loss of the capacity of dipped leaves to get the water from the plant can not be attributed to the action of arsenic on the vessels of leaves, for our experiments with penetration of stain showed that the vessels of the leaves treated with arsenic solution do not become less, but even more conductible for the water. This phenomenon can be explained only by the fact that the cells of leaf tissue lose their capacity to get water from the vessels.

4. The plasmolytic capacity of the leaves dipped in toxic arsenic solutions is unchanged for a while after removal from these solutions.

5. The death from arsenic is apparently due to the fact that the loss of water evaporated by leaves after treatment with arsenic solutions is not compensated by the access of water from the plants.

6. The inability of leaves, treated with arsenic, to obtain the water from plants is probably due to the loss of some regulators of water supply mechanism. Our experiments with ionized and colloidal arsenic solutions brought us to the suggestion that these solutions are able to extract from the plants certain substances.

7. The analysis of the arsenic solution in which the leaves were dipped showed the presence of sugar. Evidently the sugar from the leaves can escape into the surrounding arsenic solution.

8. From the arsenic solution in which the leaves soaked, we could obtain a compound containing sugar and arsenic, as indicated by the evidences: (a) with the alcohol solution described above no sugar and no arsenic could be precipitated alone, (b) the solubility of both ingredients (and especially sugar) of this substance is considerably below that of the solubility of As₂O₃ and sugar alone.

9. The injury of plants with arsenic, the so-called "burning" has nothing to do with the burning of plants due to acids or sunshine.

10. The experiments described above suggest that the injuries to the plant from arsenic may depend on the reaction between arsenic and glucids.