By placing small quantities of Li salts in the soil at marked locations between the rows of corn, and testing the tissues of the nodes spectrographically, it was possible to estimate the extent of the root systems of the plants. A summary of 4 yrs.'' results showed that all plants 40 cm. from the lithium spot contained Li, indicating their roots had penetrated to the Li core. No plants located as much as 110 cm. contained Li. Half the plants showed positive tests at 60-69 cm., which would indicate that the average root extension, by this method, was about 27 in. from the plant.