A suspension of carbon black particles was sucked in by sieve-tubes. Particles of 200-700 A were found on both sides of plates with plugged pores. This indicates that open connections of sufficient diameter must have been present during passage.

Acta botanica neerlandica

CC BY 3.0 NL ("Naamsvermelding")

Koninklijke Nederlandse Botanische Vereniging

P.M.L. Tammes, & T.S. Ie. (1971). Studies on phloem exudation from Yucca flaccida Haw. IX. Passage of Carbon black particles through sieve plate pores of Yucca flaccida Haw. Acta botanica neerlandica, 20(3), 309–317.