Plant tissue sampling might be moving away from strictly petiole sampling due to some inaccuracies.
More Inaccuracies in Petiole Sampling
Several findings coming out of Washington State University are showing that current tissue sampling methods may not be the best way to do so. Current standards sample from the petiole and nothing else. Professor of Soil Science Joan Davenport says sampling should also be taken from a storage organ like the leaf of the plant. Davenport says because the petiole acts as a straw for the leaf, it can have major inaccuracies.