The plucking of tea leaves is a fine art beginning with the starting of new growth and continuing every few days until growth stops. In certain regions growth is practically continuous and plucking also, but in most regions the plant has an obvious resting period, when it is pruned back. A properly cared for plant may last as long as forty or fifty years. In a modern tea plantation the only part of the process of tea making that involves handling is the plucking of the leaves, largely done by women and children. The leaves are then spread on racks and allowed to partly wither, after which they are put between rollers so as to crush the tissue, thereby allowing the more rapid escape of water. After rolling, all black teas are again spread out when oxidation of their juices changes their color, but green teas omit this second spreading out and sometimes even the first. The oxidation of black teas is produced by an enzyme in the juice, in green tea this process is stopped by subjecting the leaf at once to steam. This kills the enzyme but preserves the green color of the leaf. In the black tea the enzyme is allowed to work for two or three hours when the leaves are again slightly rolled to seal in the juices and the leaves are then subjected to a current of air progressively warmer until it reaches a temperature well above boiling point. Once the temperature reaches about 240 degrees the process goes on only for about twenty minutes when the leaves are perfectly dry and crisp. The different sized leaves, buds, twigs, etc., are then sorted by mechanical sifters and the finished tea is ready for packing. Experts declare that there is no difference between broken and unbroken leaves, and if there is any the flavor is probably better from broken leaves. From the upper three leaves and their bud the finest teas are made, but from adjoining plantations, even from the same plants at different seasons or different pluckings, vastly different teas are often produced. In different regions the process varies slightly in its details, and different soils and culture undoubtedly affect the flavor of tea, just as they do other crops. Some of these local conditions are of great value, and the skillful handling of the leaves is as much of a fine art as it is a science. Unlike wines, tea is best when fresh and much of the romance of the sea centers around the China clippers which made remarkably swift passages between China and England around the Cape of Good Hope. With the opening of the Suez Canal competition for increased speed became still more keen, but steam vessels took the romance out of the trade. Much of the tea used in the United States comes from Japan and does not go through London, which for over two hundred years was the tea market of the world.