Further Experiments on the Relation of Vitamin B₁to the Growth of Green Plants

Species of plants grown in sand culture under greenhouse conditions respond to addition of vitamin B1 to the nutrient solution (0.01 mg. per liter) with marked increases in rate of dry weight accumulation. A similar influence of added vitamin on dry weight accumulation of plants grown in soil is also demonstrated. 2. Carob trees supplied on alternate days with vitamin B1 in sand culture during 1 year continued to exhibit a greater growth rate than controls which did not receive the vitamin. This and other experiments indicate that the promotive effect of added vitamin is lasting rather than temporary. 3. Tomato, which does not respond to addition of vitamin B1 with added growth, was found to contain at least three times as much vitamin in its leaves as was found in the leaves of other plants (Cosmos, Poa, Brassica, etc.) which do respond to such addition with added growth. Pisum sativum, another species unresponsive to additions of the vitamin, was found to contain more than twice as high a concentration of leaf vitamin as the responsive species. It is suggested that the amount of vitamin B1 synthesized by the leaves of a given species regulates, at least in part, the response of that species to additions of the vitamin. It is possible that leaf vitamin content might be used to diagnose whether or not addition of vitamin B1 would promote the growth of a given crop or species of plant. 4. When vitamin B1 is supplied to the roots of plants grown in sand culture, the vitamin content of the leaves is increased over that of control plants not supplied with the vitamin.