Many early 19th-century accounts, including Charles Darwin's (July 1836), described the volcanic island as barren with very few plants, some of them endemic to the island, not to be found anywhere else. Scientists estimate the island's native vascular plants to be between 25 and 30 species, 10 of them endemic to Ascension. This impoverished flora is a consequence of the age of the island (only 1 million years old) and isolation (over 1,500 kilometres (930 mi) from any major landmass). Then, in 1843, the British plant collector Joseph Dalton Hooker visited the island with Sir James Clark Ross's Antarctica expedition. Hooker proposed a plan to plant the island with vegetation to attempt to increase rainfall and make life more bearable for the garrison that was stationed there. Crucially he saw the appointment of a farm superintendent as being the key to success.