Sir Hans Heysen is an acknowledged master of Australian landscape painting, with one wag quipping his iconic works did for the gum tree what Norman Lindsay did for the nude: made them famous!
To art history student Ralph Body, Heysen's skill was an embodiment of his affection for the Australian bush.
"He clearly had a deep emotional connection to his subject," Mr Body said.
"Heysen made his home in the Adelaide Hills, amongst its gums from 1908 and, even though he trained in a traditional European set of painting values, he nevertheless was an important innovator of Australian landscape painting."
But in the course of his PhD, Mr Body uncovered a cache of letters showing not everyone was enamoured with Heysen — instead seeing the artist as a potential war-time traitor.
"They are from 1915 and 1917 from the senior commissioner in Adelaide to the police officer in Mount Barker," Mr Body said.
"His loyalty is described as being of a highly doubtful character and they request his home be put under surveillance based on little more than anonymous stories the commissioner had heard, and the fact Heysen was German-born."
World War I was in full swing.
With patriotic fervour sweeping the country, times were tough for Australians of German background.
German language newspapers were banned and German language schools were closed.
Heysen put under surveillance
Historian Michael Wohltmann has done a study of how people with German ancestry were treated.
"There's the story from Adelaide University that students tarred and feathered one of the professors simply because of his German background," Mr Wohltmann said.
"Thankfully cooler heads prevailed when it came to a proposal to strip Germans of academic qualifications they'd earned in Australia."
Heysen Gallery curator Allan Campbell said Heysen's brother-in-law was sent to an internment camp, as were many other people.
"He was interned up in Sydney, it was a terribly difficult time for the family," Mr Campbell said.
"He [the brother-in-law] wasn't released until 1920, years after the war ended."
Mr Campbell said the police letters were a revelation to both him and the current day Heysen family, who had no idea their famous forebear was under formal surveillance.
Both the curator and the student agreed one of the most striking characteristics of the correspondence is its logic, or rather lack thereof.
'One of life's great gentlemen'
Heysen had given generously to the South Australian wounded soldiers' fund, but police thought it was just a ruse.
Mr Body quotes the police reaction to reports Heysen was pleased Germany was losing.
"One day when one of my informants passed Mr Heysen working, he called out, 'the war situation looks better, the British are too good for the Germans and are giving them hell'. From this it will be seen that although Heysen's sympathy may be with the Germans, he is too clever and cunning to show any sign of disloyalty," the report read.
"The police for not one moment believe he is loyal [to the British Empire]," the report stated.
Mr Campbell describes the report as touched with a brush of hysteria.
"Where on Earth did they get that language from?
"I mean calling Heysen shrewd and cunning, it's ridiculous. He was one of life's great gentlemen and a pacifist to boot."
Mr Campbell said some art galleries took Heysen's paintings down during the war.
Mr Body also found the Art Gallery of New South Wales conspicuously left Heysen out of a major 1918 retrospective of Australian artists — one of the first held in the country.
Nevertheless after the war Heysen's reputation not only rebounded but grew: the public couldn't get enough of those beautiful gum trees.
The reaction to the Heysen family during World War II was remarkably different — and riddled with irony.
"His daughter Nora Heysen, was made one of the official war artists, the first woman in Australia to hold the job," Mr Body said.
"She was stationed in New Guinea and one of the places she painted was Finschafen, which as the name suggests was a German settlement."
For its part, in 1940 the Art Gallery of South Australia appointed Hans Heysen a trustee.
He served a record 28 years, until his death in 1968.