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Introduction
De Souza et al. showed that the growth and yield of lettuce could be improved by treatment of its seeds before they were grown, using rectified sinusoidal non-uniform electromagnetic fields. [1] It was observed that magnetism has effects on lettuce at the nursery, vegetative, and maturity stages, including a significant increase in root length and shoot height, a greater growth rate, and a significant increase in plant height, leaf area, and fresh mass. Positive biological effects of magnetism on sunflower and wheat seedlings weights were reported. [2] Further data show that the magnetic field induced by the voltage of a specific waveform enhanced or inhibited mung bean growth, depending on the frequencies, [3] which suggests that the magnetic field on plant growth may be sensitive to the waveform and frequency of the source electrical voltage. The effect of static magnetic field on plant growth has also been studied. Cakmak et al. found that static magnetic field accelerated germination and early growth of wheat and bean seeds. [4] Vashisth et al. obtained similar results with chickpeas; furthermore, they found that the responses of the plant to static magnetic field varied with field strength and duration of exposure with no particular trend. [5] However, as indicated by a literature review, weak magnetic field exhibited negative effects on plant growth, such as inhibition of primary root growth, in some cases. [6] For instance, exposure to magnetic field inhibited early growth of radish seedlings with decrease in the weight and leaf area. [7] An interesting result is that the biological effect of a magnetic field is different between the south and north poles, as illustrated by a study, which showed that radish seedlings had a significant tropic response to the south pole of the magnet, but insignificant response to the north pole. [7] It is theorized that the south pole of the magnet enhances plant and bacterial growth by conferring energy, whereas the north pole retards their growth. Thus, it is possible to utilize the magnetic north pole against infections or tumor growths. Morphological anomalies in pollen tubes of a particular plant exposed to magnetism were observed, [8] which raises an important question of whether magnetism can cause gene mutation and cancer. This issue is still controversial and...