Complex sentence: In 1834, aged 16, he drew up a neatly written list of all the plants he had found around Ganthorpe--arranged alphabetically and containing 403 species, the gathering and naming must certainly have occupied some years.
Split into simpler sentences: In 1834, aged 16, he drew up a neatly written list of all the plants he had found around Ganthorpe. Arranged alphabetically and containing 403 species, the gathering and naming must certainly have occupied some years.