In 1825 John Stevens Henslow, Charles Darwin's teacher at Cambridge, succeeded Martyn as professor of botany and soon realized that a larger site, farther from the centre of Cambridge, was desirable for the Botanic Garden. In 1831 the University purchased the present site of about 40 acres to the south of the town on the Trumpington Road, and in 1846 the first tree was planted. It had been the intention to lay out the whole 40 acres as a Botanic Garden, but presumably funds were lacking, and in fact only 20 acres were planted, the remainder being let out as allotments.