Unlike the farmer, the market gardener has to produce one crop after another throughout the year. To make up for the absence of sufficient sunshine he has to resort to “forcing” in many cases, but unfortunately this process, besides being costly, generally results in the production of a crop of inferior quality. Evidently the work of the market gardener would be greatly facilitated by some artificial substitute for sunshine, to keep his plants growing properly in dull weather. In 1880, Sir William Siemens, knowing that the composition of the light of the electric arc was closely similar to that of sunlight, commenced experiments with an arc lamp in a large greenhouse. His idea was to add to the effects of the solar light by using the arc lamp throughout the night. His first efforts were unsuccessful, and he discovered that this was due to the use of the naked light, which apparently contained rays too powerful for the plants. He then passed the light through glass, which filtered out the more powerful rays, and this arrangement was most successful, the plants responding readily to the artificial light. More scientifically planned experiments were carried out at the London Royal Botanic Gardens in 1907, by Mr. B. H. Thwaite, and these showed that by using the arc lamp for about five hours every night, a great difference between the treated plants and other similar plants grown normally could be produced in less than a month. Other experiments made in the United States with the arc lamp, and also with ordinary electric incandescent lamps, gave similar results, and it was noticed that the improvement was specially marked with cress, lettuce, spinach, and other plants of this nature. In 1910, Miss E. C. Dudgeon, of Dumfries, commenced a series of experiments with the Cooper-Hewitt mercury vapour lamp. Two greenhouses were employed, one of which was fitted with this lamp. Seeds of various plants were sown in small pots, one pot of each kind being placed in each house. The temperature and other conditions were kept as nearly alike as possible in both houses, and in the experimental house the lamp was kept going for about five hours every night. In every case the seeds in the experimental house germinated several days before those in the other house, and the resulting plants were healthy and robust. Later experiments carried out by Miss Dudgeon with plants were equally successful.