It is well known that environmental factors such as light, gravitation, electric fields, and chemical gradients can stimulate oriented growth of individual cells [1, 2]. Oriented growth of whole plant organs in magnetic fields was first observed by Audus [3] and subsequently called "magnetotropism". He found that if cress roots or oat shoots were placed in an inhomogeneous magnetic field these organs grew toward the regions of decreasing field strength. He filso demonstrated [4] that this oriented growth could not simply result from the diamagnetic force acting on the plant organ in a magnetic field gradient. No alternative explanation of this effect was given, and at present the physiological processes causing the phenomenon of magnetotropism of multicellular systems are still unknown. As indicated by Audus, cell divisions might be a prerequisite for the magnetotropism of plant organs. In order to find out whether cell divisions are necessary for magnetotropism, we tested the effect of magnetic fields on the elongation growth of individual cells the pollen tubes of Lilium longiJlorum. Their growth physiology and their ultrastructure are rather well known. For example, a number of investigations in the past few years have shown that the growing lily pollen tubes accumulate ~SCa at their tips [5, 6] and that they generate a transcellular electric current that seems necessary for the elongation of the tube [7]. In electric fields of 5-6 V/cm most of the tubes germinate at the anodal side of the grains and afterward grow parallel to the applied field [8; Pollen grains of L. longiflorum were sputtered with a fine brush onto the bottom of dishes of Plexiglass (25 x 25 x 5 mm). Then growth medium of 33 ~ containing 300 m M mannitol, 1.65 m M CaC12-2H20, 1.0 m M KNOa, 0.13 m M H3BOs, pH 5.15.3 [9], and 2% agar was carefully poured over the grains. Most of the grains adhered to the bottom of the chamber and were fixed in place by the hardening agar. The dishes were then placed immediately in the 50-mm-wide bore of a horizontal Bitter