Ventilation finds its chief significance as a means of controlling temperature and humidity, though actual change of air may be a factor. High soil moisture, high humidity, high temperature, and faulty ventilation, all favor the ravages of the various damping-off fungi mentioned above which cause little plants to rot off near the ground. Transplanting The main advantage of transplanting plants before they are set in the field is to give them increased space, or, in other words, to conserve space in greenhouses and frames. Other advantages have been claimed, but in many instances the gains have resulted from more space rather than from the actual shift. Transplanting checks growth through breakage and disturbance of the root system. Loomis[14] finds that "the immediate effect of transplanting is a reduction in the water supply, and the immediate and long-time results are dependent upon the severity and duration of such reduction." Transplanting has little effect upon very young plants and a shift at the age of six or eight weeks checks the plant about as much as two earlier transplantings. The tomato falls in the group of plants that stand transplanting well, roots being rapidly replaced. Transplanting breaks roots and so results in the growth of branches which are shorter than the members of the old system. The new system is accordingly less severely damaged in later transplantings. To insure efficiency, the work of transplanting merits careful attention. Carelessness as to details means loss through unevenness of plants. For example, if soil is not carefully packed at the edges and corners of the flats, irregular water supply and irregular growth result. If much transplanting is to be done, it pays to divide up the work, as is done in a factory. Have a good place for doing the work--a warm, light, and comfortable room. Tired workers are not efficient. Spotting boards are of service if properly made and correctly used. Soil should always contain just the right degree of moisture to allow holes to stand open. Care must be taken that the workers in setting plants do not double the roots or close the holes at the top leaving the roots dangling in an open space below. It is said that a good worker will prick out 10,000 plants per day, though everything must be convenient to accomplish this and many growers regard 6,000 plants as a good day's work. Pruning Young Plants Pruning of tops injures rather than helps the plant, for it destroys leaves which are the machines that make carbohydrates, the principal material for growth. Pruning to cure legginess is bad. Proper management of time, temperature and water will provide adequate control and if plants should become leggy, it is better to plant them by laying them down in a trench with a few inches of top above ground than it is to prune them.