In 1926 Mason (1) drew the attention to the fact that in the nodes of the stem of the Dioscoreaceae special xylem and phloem structures are found which join respectively the xylem and phloem elements of the vascular bundles running in the successive internodes. He called these structures wood plexus and phloem plexus. Especially the phloem plexus was further described by him. Mason’s results can be briefly summarized as follows. The sieve tubes of the successive internodes do not join up with each other directly, but via a glomerulus, a great number of oblong thin-walled parenchymatous cells running fairly parallel, with a distinct nucleus and densely plasmatic contents. These glomeruli are connected with the ends of outgoing and incoming sieve tubes by similar cells (bast tubuli) lying less compactly and being according to the distance to be bridged, of different lengths. On the ground of this anatomic structure, Mason concludes to a secretory function of the glomeruli, thinking it at the same time probable that these glomeruli form an obstacle for a rapid moving of carbohydrates along the phloem. Whereas, therefore, a mass transport in the internodes through the sieve tubes is conceivable, the substances transported through the phloem must pass the plasm at the nodes. An analogous case Schumacher (2) sees in the anatomical relations, as they appear in the haustorial connections of the parasite Cuscuta odorata on Pelargonium Zonale.