Effects of combined DC and AC magnetic fields on germination of hornwort seeds

Seeds of hornwort ( Cryptotaenia japonica Hassk ) were exposed to sinusoidally time‐varying extremely low frequency (ELF) magnetic fields (AC fields) in combination with the local geomagnetic field (DC field). Exposure lasted 24 h/day for 16 days. Three directions of the AC magnetic fields were considered; the vertical (magnetic flux density $\vec B_{ACV}$ ), the directions parallel ( $\vec B_{AC||}$ ), and perpendicular ( $\vec B_{AC \bot }$ ) to the direction of total geomagnetic field (magnetic flux density $\vec B_G$ ) in the geomagnetic plane (GP). Controls consisted of seeds exposed to zero AC magnetic fields in combination with the DC magnetic field. The $\vec B_{ACV}$ in combination with $\vec B_G$ effectively promoted the germination of hornwort seeds when applied at 750 μT (RMS) at 7 Hz or 500 μT (RMS) at 14 Hz from among the cases of individual frequencies f  = 3.5, 7.0, 10.5, 14.0 Hz at 500 and 750 μT. The $\vec B_{AC||}$ promoted the germination of hornwort seeds more effectively than the $\vec B_{AC \bot }$ in combination with $\vec B_G$ when 500 and 750 μT at 7 Hz were applied. Bioelectromagnetics 25:552–559, 2004. © 2004 Wiley‐Liss, Inc.