The sole objects of nutrition being to repair waste and to admit of growth, Nature has so arranged that within certain limits it is always most vigorous when growth or waste proceeds with the greatest rapidity. Even in vegetables this relation is distinctly observable. In spring and summer, when vegetative life is most active, and when leaves, flowers, and fruit, are to be formed, and growth carried on, nourishment is largely drawn from the soil, and the elaboration and circulation of the sap are proportionally vigorous; whereas in winter, when the leaves and flowers have passed away, and vegetable life is in repose, little nourishment is needed, and the circulation of the sap is proportionally slow. In accordance with these facts, every one will recollect how freely a shrub or a tree bleeds, as it is called, when its bark is cut early in the season, and how dry it becomes on the approach of winter. It is the activity of the circulation in summer which renders its temporary suspension by transplanting so generally fatal at that season; whereas, owing to the comparative sluggishness with which it is carried on in winter, its partial interruption is then attended with much less risk. In vegetables, the quantity of nourishment taken in entirely depends on, and is regulated by, the circumstances in which they are placed. When they are exposed, as in spring and summer, to the stimulus of heat and light, all their functions are excited, waste and growth are accelerated, and a more abundant supply of nourishment becomes indispensable to their health and existence; and hence, in a dry soil incapable of affording a copious supply of sap, they speedily wither and die. Exposed to cold, on the other hand, and shaded from the light, their vitality is impaired, and the demand for nourishment greatly diminished. This is uniformly the case in winter; and many circumstances shew that the change is really owing to the causes mentioned above, and not to any thing inherent in the constitution of the vegetable itself. In tropical climates, for example, where heat, light, and moisture abound, vegetable life is ever active, and the foliage ever thick and abundant; and even in our own northern region, we are able by artificial heat so far to anticipate the natural order of the seasons, as to obtain the ripened fruit of the vine in the very beginning of spring. The whole system of _forcing_ vegetables and fruit, so generally resorted to for the early supply of our markets, is, in truth, founded on the principle we are now discussing; and by the regulated application of heat, light, and moisture, we are able to hasten or to retard, to a very considerable extent, the ordinary stages of vegetable life. But to ensure success in our operations, we must be careful to proportion the supply of nourishment to the state of the plant at the time. If, by the application of heat, we have stimulated it to premature growth and foliage, we must at the same time provide