Stoklasa (1896, 1898) again found that phanerogamic plants can withstand arsenic poisoning for some time in the dark or in CO₂-free air, provided that glucose is given in the food solution. The arsenic poisoning is at its maximum during carbon assimilation by means of chlorophyll. The toxic action of arsenious and arsenic acids, especially in phanerogams, is due to injury to the chlorophyll activity. The destruction of the living molecule is far more rapid in the chlorophyll apparatus than in the protoplasm of the plant cell. Thus it seems that the physiological cause of the toxicity of arsenic is partly a direct action on the root protoplasm, whereby its osmotic action is hindered, and partly a detrimental action upon those functions which are directly concerned with the elaboration processes of nutrition. 2. _Effect of arsenic compounds on germination._ In view of the great toxicity of arsenic to plants in their various stages of development, one would naturally expect to find a similar action with regard to the germination of the seeds. Davy (1859) casually mentioned cases in which watering with arsenical solutions or dipping seeds in arseniated water prevented germination. Heckel (1875) found that arsenious acid checks germination and kills the embryo at relatively feeble doses, ·25 gm. to 90 gm. water.[10] Guthrie and Helms (1903–4–5) carried out a systematic series of experiments to test the effect of arsenic compounds upon different farm crops. Various amounts of arsenious acid were added to soil in pot experiments, and the seeds of the several crops were then sown. With barley, wheat and rye 0·10% arsenious acid had little or no effect on germination, while an increase in the poison exercised a retarding action. Maize could withstand 0·40% arsenious acid without retardation being perceptible. The aftergrowth with the different crops varied considerably. The wheat plants with 0·10% arsenious acid grew all right at first, but later on they developed weakly. The toxic action increased rapidly as the strength of the poison rose in the different pots. Barley proved even more sensitive than wheat, for even 0·05% arsenious acid affected the growth adversely. After a time the plants with 0·05–0·06% recovered and grew strongly, though not so well as the controls, but those with 0·10% practically died off. Rye behaved in the reverse way from wheat. The plants with 0·10% were slightly checked at first but later recovered and made growth quite equal to the check plants. Growth was stunted with 0·20% arsenious acid, and the plants were killed with 0·30%, so that rye is far less sensitive than barley. With maize the growth was slightly affected with 0·05% As₂O₃, and increasingly so with greater quantities. It was also found that the action of 0·8% As₂O₃ was strongly adverse to the germination of all plants, and that above this strength germination was altogether prevented.