Plant specialist Dustin McMahon hand-pollinates genetically modified corn plants inside greenhouses on the roof of Monsanto agribusiness headquarters in St Louis in 2009. Bayer said Monday that it had offered to buy Monsanto for $62 billion in cash. (Brent Stirton/Getty Images.)

The German pharmaceutical giant Bayer announced Monday that it had offered $62 billion to acquire Monsanto, potentially pushing the iconic maker of aspirin and Alka-Seltzer further into the world of genetically modified seeds and agricultural chemicals.

The unsolicited offer, if accepted by St. Louis-based Monsanto, would create the world’s largest agrochemicals company. The 115-year-old Monsanto would be absorbed into the overseas giant, Bayer, bringing with it the herbicide Roundup and a controversial history as one of the first companies to create a genetically engineered seed.

Better known for its pharmaceutical business, Bayer has also built a large agricultural business. It already sells seeds as well as chemicals that kill weeds and bugs. And company officials said Monday that Monsanto would be a good fit for that business.

“Together we would draw on the collective expertise of both companies to build a leading agriculture player with exceptional innovation capabilities to the benefit of farmers, consumers, our employees and the communities in which we operate,” Werner Baumann, chief executive of Bayer, said in a statement.

It is unclear whether Monsanto would accept the offer or whether U.S. regulators would balk at the creation of such a large industry competitor. Bayer only made its proposal public after Monsanto issued a statement late last week in response to speculation and media reports that it had received an offer, which it declined to describe. Bayer sought to quell speculation about the terms of its deal, saying it was making an all-cash bid.

In a statement, Monsanto said it was reviewing the proposal.

Bayer said the combined company would be able to achieve cost savings of about $1.5 billion over three years. It is offering $122 a share for Monsanto, a 37 percent premium over Monsanto’s closing price on May 9, the day before it submitted its offer.

The offer comes amid a consolidation boom in the chemicals market. Late last year, Dow Chemical and DuPont agreed to merge into a $130 billion behemoth, then split again into three companies. And Chinese state-owned China National Chemical plans to buy Syngenta for $43 billion. Monsanto had made a failed attempt to buy Syngenta.

Sales at seeds companies have suffered recently. U.S. farmers are not spending as much amid falling commodity prices, and a strong U.S. dollar has made overseas sales tougher.

“We’re intrigued by the deal,” said James Zoldy, president of Halsey Associates, which owns more than 100,000 Monsanto shares. “You have a company that was the hunter, Monsanto . . . that has become the hunted here.”

If Monsanto decides to negotiate with Bayer, the company’s board is likely to push to raise the price of the deal, he said.

Regulators may also object to the creation of such a large market competitor, analysts said.

“What complicates this is the whole regulatory backdrop is potentially problematic,” said Zoldy. “There has been a significant shake-up in industry structure here. The entire industry structure has become more concentrated. . . . Regulators are always quite sensitive to that.”

The Obama administration has become increasingly aggressive at enforcing antitrust rules over the past year. The Justice Department has blocked a combination of media goliaths Comcast and Time Warner Cable, and the Federal Trade Commission stymied Staples’s $6.3 billion acquisition of Office Depot.

Perhaps in anticipation of such scrutiny, Bayer said in a statement that the combination would be “truly complementary from a geographic perspective.”

In a May 10 letter to Monsanto’s chief executive Hugh Grant, Bayer said it has a “successful track record” in working with regulators. “We have analyzed the potential regulatory aspects and are very confident that we will be able to obtain all necessary approvals in a timely manner,” the letter said.

Bayer said it planned to finance the deal with a combination of debt and equity to be repaid quickly by the “strong cash flow” generated by the combined business. The Associated Press reported that some Bayer shareholders expressed concerns about the new shares and whether it would dilute their holdings. Others worried about an expansion away from Bayer’s core pharmaceutical business, especially into the world of genetically modified crops. Some countries have blocked such seeds, and the business had been a target of environmental activists.

Bayer’s stock fell about 5.7 percent Monday. Monsanto’s rose about 4.4 percent.