Data Views Total Plants: 81 CSV Excel PDF , Previous12345 Show all rows. Paginate rows. Click on column headings to sort table by that column Plant Part All Bark Bulb Fruit Leaf Plant Root Root Bark Seed Shoot Stem Tuber Low PPM High PPM StdDev *Reference Zea mays Seed 0.06 63.0 1.6 * *Unless otherwise noted all references are to Duke, James A. 1992. Handbook of phytochemical constituents of GRAS herbs and other economic plants. Boca Raton, FL. CRC Press.