Journal of Experimental Botany (1971), 22, 735-740
by Rupert Sheldrake

Cambium and differentiating xylem and phloem tissues from the trunks of trees of Acer pseudoplatanus L., Fraxinus excelsior L., and Populus tremula L. were extracted with ether and tested for auxin, which was found on chromatograms of the acidic fraction at an Rf corresponding to that of indol-3yl-acetic acid in five solvent systems. In addition, small amounts of auxin with a higher Rf in ammoniacal isopropanol were found in phloem samples. The amounts of auxin were greatest in xylem samples, less in the cambium, and least in phloem. The differences, which cannot be explained in terms of differential losses during extraction and purification, suggest that auxin is actually formed in differentiating xylem tissue. The significance of these results is discussed.