During the whole period there was a great lack of specie, which in the early years had not been a very serious drawback, as barter was the ordinary method of exchange, but as the colonies advanced in importance it was a decided check upon foreign commerce. In 1631, Massachusetts declared corn to be legal tender, and four years later it was ordained that public dues were to be paid in this commodity at the rate of 6s. per bushel. This system was employed in the next decade by both Connecticut and Newhaven, with decidedly disadvantageous results, for it brought about the inconvenience of a double price; the monetary payment being about half the actual value of the payment in kind. For many years in the Indian trade the settlers had used Indian shell money or wampum. This medium of exchange was first applied in New Plymouth in 1627, and was afterwards employed by Coddington when he bought Aquedneck. In 1641, wampum was declared legal tender under £10, but within eight years the Massachusetts Assembly refused to accept it for taxes. The fact was that it depended solely upon Indian trade, and when this began to decline, wampum was valueless. Rhode Island was the last colony to discontinue its use for taxes, which it did in 1662; though it acted as small change in Newhaven well into the eighteenth century. As early as 1642, Massachusetts, by means of its foreign trade, began to obtain coined money in the shape of Dutch ducats and rix-dollars. But the extraordinary mixture of coins was very awkward, so that in 1652 a mint was established in the colony. John Hall, the goldsmith of Boston, was made its master. The coins had stamped upon them the word Massachusetts encircling a tree, which was in early years a willow, later an oak, and finally a pine. Charles II. was furious at this attack upon his coinage, and the story goes that to appease his wrath he was told that the emblem of the oak was in grateful memory of his glorious escape at Boscobel.