Given the task definition and input, reply with output. In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.

Passage: Persoonia terminalis was first reported by Lawrie Johnson of the Royal Botanic Gardens, Sydney, in the 1981 edition of Flora of New South Wales. He viewed it as a distinctive subspecies of Persoonia nutans, a broadly defined species that included many forms since classified as distinct. Queensland botanists Trevor Donald Stanley and Estelle M. Ross classed P.terminalis as part of Persoonia oxycoccoides in their 1983 work Flora of South-eastern Queensland. They considered it more likely a species in its own right, as they believed the description of the Queensland populations did not match the P. oxycoccoides from central New South Wales. Upon re-examining Persoonia nutans and Persoonia oxycoccoides, Johnson and Peter Weston concluded that there were in fact several distinct species, and that Persoonia terminalis was described as such in 1991. The type specimen was collected south of the Torrington pub on the EmmavilleTorrington road by Weston and ecologist Peter Richards, and is now housed in the National Herbarium of New South Wales, which is part of the Royal Botanic Gardens and Domain Trust Sydney and Office of Environment and Heritage. The Herbarium houses over 1.2million other specimens. The generic name Persoonia is derived from the name of South African botanist Christiaan Hendrik Persoon. The specific name terminalis refers to the inflorescences (clusters of flowers) that are in this species at the ends of the branchlets. Its common name is the Torrington geebung.
Link Information: Lawrie Johnson, was an Australian taxonomic botanist. He worked at the Royal Botanic Gardens, Sydney, for the whole of his professional career, as a botanist (19481972), Director (19721985) and Honorary Research Associate (19861997) Answer: 33
How long had Johnson been working at the Gardens?