630. The Chelsea botanic garden seems to have existed about the middle of this century. In 1685, Evelyn visited Watts, the head-gardener. 'What was very ingenious, was the subterranean heat conveyed by means of a stove under the conservatory, all vaulted with brick, so that he has the door and windows open in the hardest frosts, excluding only the snow.' (Memoirs, &c., vol. i. p. 606.) In Watts's garden was a tulip tree, and in the hothouse what Ray calls a tea shrub, though it certainly was not the Chinese tea tree. (Ray's Letters.) The ground occupied by this garden was rented from Sir Hans Sloane, who afterwards, in 1722, when applied to for a renewal of the lease, gave the freehold of the ground (more than four acres) to the Company of Apothecaries, on condition that the demonstrator (who gave lectures to the young men studying for apothecaries) should deliver annually to the Royal Society fifty new plants, all specifically described, till the number should amount to 2000, which it was then supposed would be sufficient to exhaust the then unexplored sources of nature. A list of the new plants introduced was published every year in the Philosophical Transactions, till 1773, when 2550 having been presented, the custom was discontinued - the number of plants mentioned having been introduced in less than fifty years. Since that period, upwards of 30,000 plants have been introduced, and the number is increasing daily.