Lawyers for agribusiness titan Monsanto Co. drew pointed questions from the Canada Supreme Court on Tuesday in a dispute with a Saskatchewan canola grower that has become a cause for biotechnology opponents and proponents around the globe.

The court could takes months to rule on the dispute, which began in 1997 when Monsanto discovered its canola plant, genetically engineered to withstand the company's popular weed killer, growing on Percy Schmeiser's farm.

The suit alleges Schmeiser obtained Monsanto seeds without paying for them. Schmeiser contends the company's canola accidentally took root on his farm, possibly falling from a passing truck or arriving with a gust from a neighboring farm.

Two lower courts found in Monsanto's favor and ordered Schmeiser to pay the company about $140,000 in damages and legal costs.

Some farmers, especially those from developing nations, fear that natural or accidental contamination of their conventional crops with biotech varieties will give biotech companies licenses to seize their crops.

"This exposes countless farmers to potential liability," argued Steven Shrybman, who is representing the Washington, D.C.-based International Center for Technology Assessment and five other activist groups who joined the Canada Supreme Court case in support of Schmeiser.

Schmeiser's lawyer argued that in light of another court ruling refusing to patent "a higher life form" -- a genetically engineered mouse created by Harvard University -- Monsanto's patent on the engineered gene in canola does not give it ownership of the entire plant.

Robert Hughes, Monsanto's lawyer, argued that the company wasn't seeking a patent on the entire canola plant, but rather an "ingredient" of the plant. He likened the company's patent to that of an inventor who develops a new kind of steel for automobiles and receives a patent for that component rather than the whole car.

"According to the Harvard Mouse ruling, I don't think the steel analogy works," countered Supreme Court Justice Louise Arbour.

Though the nine-judge panel's leaning was inscrutable, industry lawyers were peppered with even sharper questions than the other side.

Justice Ian Binnie appeared skeptical of the damage award, asking what additional profit Schmeiser made with Monsanto's seeds than conventional seeds if Schmeiser, as he has testified, didn't spray the company's herbicide.

Monsanto's lawyers were also rebuffed when arguing that Schmeiser's fields contained such a high percentage of genetically engineered plants -- as much as 98 percent -- that no innocent explanation could explain how Monsanto's canola ended up in the farmer's field.

"There is no evidence that Mr. Schmeiser bought the seeds," snapped Justice Louis LeBel, to the delight of Schmeiser's supporters in the packed courthouse.

Monsanto and its backers who joined the case -- an industry lobbyist and two farm groups -- argued that invalidating the company's patent could do it and the country economic harm and undermine Canada's patent system.

"Patents create a climate that favors new research," argued A. David Morrow, a lawyer for the Canadian Seed Trade Association, who said his organization "is in favor of biotechnology research and therefore in favor of strong Canadian patent protection."

Monsanto and its backers insist Schmeiser must pay every year for seed, just like 30,000 other canola farmers in Canada, where roughly half the 10 million acres of canola have been converted since 1996 to Monsanto's variety.

"This patent makes us more profitable and better farmers," argued Mona Brown, a lawyer with the Canadian Canola Growers Association.

A ruling against Monsanto could boost the anti-biotechnology movement, which is trying to stop the spread of genetically engineered plants and animals until more comprehensive scientific studies are conducted to ensure the technology is safe.

Outside court, Schmeiser said he was relieved his five-year legal battle, which has cost him more than $230,000 in legal bills, is nearly over.