We studied the effects of weak and extremely-low-frequency (ELF) magnetic fields (MFs) on the growth and germination of spruce seedlings Picea abies (L.) Karsten simultaneously exposed to stress conditions. The drought environmental stress conditions were simulated by watering the seedlings with polyethylene glycol (PEG) at two different concentrations: 88 and 176 g/L. The experiments showed that a weak homogenous sinusoidal magnetic field (50 Hz, 25 and 100 microT, 12 h/day), computer controlled and generated by a pair of Helmholtz coils, strongly inhibited the germination and mass growth of seedlings, while under normal conditions (without PEG) the effects were either zero or stimulatory. When the seeds were soaked in water, the effects of MF were reverse, i.e. they were stimulatory. This strongly supports some previous findings of other authors that biological systems under stress may demonstrate higher sensitivity to extremely low-frequency electromagnetic fields (EMFs), but as far as we know, so far these findings have not
been subject to any further systematic research. Our experiments demonstrate the inhibition of germination was greater at the greater concentration of PEG (at 100 microT), while the growth as well as fresh weight did not show this concentration dependence. Besides well known frequency and power windows we suggest the physiological windows as well, since even the quality of
responsiveness to MFs (i.e. stimulation or inhibition) may strongly depend on the physiological state of organisms, as it was already proposed by some other authors and our group.

The following graph represented the effect of magnetic field 50 Hz 100 microT on the germination of seedlings under stress and nonstress conditions.