WATERING, in Horticulture, the process of applying water arti ficially to plants. Water in a greater or leas quantity is necessary to the existence of the whole vegetable kingdom : not only do the ele ments of water enter into the composition of the tissues of plants, but by its agency the various saline ingredients, as well as certain gases that enter into the composition of vegetable tissues; are carried into the plant. Water also exerts an influence on the temperature of the soil and of the plants to which it is applied. It is on these accounts that the application of water to plants is an important process in horti culture, more especially in the hothouse and greenhouse. During winter plants require little moisture, as the processes of life are at that period very inactive, but at the same time a small quantity is required in order to meet the demands of approaching activity. If plants are supplied with too much water during winter, their tissues become distended, end the whole plant is enfeebled. The largest supply of water is required when plants are growing rapidly and at the season when they are putting forth their leaves. When plants have ceased to grow, or when the leaves and flowers have ceased to expand, they require less water. When however the object in the culture of plants is to render either their leaves or fruits as succulent as possible, they should be supplied with abundance of water. This is done with spinach, lettuce, and other der:meow.] plants, and by this means their tissues are rendered more tender, and their peculiar secretions, which are often disagreeable, are diluted. The same thing is done in the cultivation of the strawberry, where the object is to render the fruit as large as possible. In this case however the large size of the fruit is obtained at the expense of its flavour. Even plants bearing succulent fruits, as the melon, &c., may ho over-watered, and the flavour of their fruit destroyed. In supplying water to all plants due regard should be had to temperature, as, cwteris paribus, plants require more water in proportion as the temperature is higher.
Although the supply of water artificially to plants cultivated in houses is obviously necessary, there is some doubt as to whether it is required by plants growing in the open air, where they are exposed to natural supplies. Professor Lindley, in his ' Theory of Horticulture,' says, " It is indeed doubtful whether watering plants in the open air is not often more productive of disadvantage than of real service to plants." At the same time the practice is at present very general, and there are some advantages in it, independent of supplying plants with water. It is frequently very effectual for removing insects from the
leaves of plants, and also for removing dust and dirt in exposed situa tions. Mildew is also prevented in annuals by abundant watering. The fungi which produce or are found on mildewed peas, and those which destroy the spinach and onion, may be removed by abundant watering. Where the leaves of plants are watered, this should never be done whilst the sun is shining upon them, as this increases the evaporation. The morning and evening are the best times for watering plants; but where it is necessary to do this in the middle of the day, the roots alone should be watered. After transplanting, whether of one of the greatest improvements effected of late years in the eon atruction of overshot water-wheels consisted in the introduction by Mr. Fairbairn of the ventilating buckets. The diameter of the wheel, , of course, should be made as nearly as possible equal to the height of the fall, and the velocity of the wheel kept to about the rate of 3 feet per second, measured on the outer edge. A greater velocity would pro duce a centrifugal force in the water contained in the buckets, which would to some extent diminish the useful effect of the wheel. The best overshot-wheels, in which the water is conducted upon the wheel carefully, and the tail-bay of the channel built eo as not to interfere with the escape of the water, yield an effective result of 015 e u ; and they are, therefore, constantly used when a sufficient fall can be obtained for their establishment. In some mining districts overshot wheels of as little ale 8 feet in diameter are used ; but they do not yield even so good results as the best breast-wheels in close races. A fall of 16 fact seems, in fact, to be about the minimum fall able to produce the full amount of dynamical force an overshot-wheel is able to yield. As to the bad-shot-wheels, they do not involve any other principle than the overshot-wheels ; nor, indeed, can they be considered to offer any advantage over the latter, unless in some peculiar cases, wherein the motion of the machinery may require the revolution of the wheel to take place in one particular direction ; and wherein the water is required to be brought upon the back part of the wheel. Sometimes, it may also be added, there may be an advantage gained by the use of the backshot-wheel, if the tail-bay should be exposed to be flooded, or to receive backwater ; because in such a case the revolution of the wheel would still be in the direction of the natural current., and the backwater would not oppose the passage of the buckets co seriously as would be the case with a true overshot-wheel.