The air surrounding the Earth is always charged to some extent with electricity, which in fine weather is usually positive, but changes to negative on the approach of wet weather. This electricity is always leaking away to the earth more or less rapidly, and on its way it passes through the tissues of the vegetation. An exceedingly slow but constant discharge therefore is probably taking place in the tissues of all plants. Experiments appear to indicate that the upper part of a growing plant is negative, and the lower part positive, and at any rate it is certain that the leaves of a plant give off negative electricity. In dull weather this discharge is at its minimum, but under the influence of bright sunshine it goes on with full vigour. It is not known exactly how this discharge affects the plant, but apparently it assists its development in some way, and there is no doubt that when the discharge is at its maximum the flow of sap is most vigorous. Possibly the electricity helps the plant to assimilate its food, by making this more readily soluble. This being so, a plant requires a regular daily supply of uninterrupted sunshine in order to arrive at its highest possible state of maturity. In our notoriously variable climate there are many days with only short intermittent periods of bright sunshine, and many other days without any sunshine at all. Now if, on these dull days, we can perform at least a part of the work of the sunshine, and strengthen to some extent the minute currents passing through the tissues of a plant, the development of this plant should be accelerated, and this is found to be the case. Under electrical influence plants not only arrive at maturity quicker, but also in most cases their yield is larger and of finer quality. Lemström used a large influence machine as the source of electricity in his experiments in electro-culture. Such machines are very suitable for experimental work on a small scale, and much valuable work has been done with them by Professor Priestly and others; but they have the great drawback of being uncertain in working. They are quite satisfactory so long as the atmosphere remains dry, but in damp weather they are often very erratic, and may require hours of patient labour to coax them to start. For this reason an induction coil is more suitable for continuous work on an extensive scale.