The Phloem: A Case of Theory Against Experiment

The history of the long-distance transport systems of vascular plants, phloem, and xylem, is a long and winding road of scientific progress which fascinated and occupied foresters, botanists, and physicists during the last 250 years. Although the Munch pressure flow hypothesis of phloem transport is meanwhile generally accepted, some details are not yet really understood. This pertains especially to the sieve plates whose function within the sieve tubes is controversially debated. Recently, Nakad et al. (2023, https://doi.org/10.1029/2022jg007361) contributed a fresh interpretation of the sieve plates based on a simple experimental setup which allowed to study their effect on phloem flow.