BERLIN • Chemicals giant Bayer made an unsolicited US$62 billion ($85.6 billion) all-cash offer to acquire Monsanto and create the world's biggest supplier of farm chemicals and genetically modified seeds, disclosing the terms of its bid amid investors' growing concern that it might overpay.

Bayer offered US$122 a share in an all-cash bid in its May 10 written proposal, the Leverkusen-based company said in a statement yesterday.

That is a 37 per cent premium to Monsanto's May 9 closing price. The payment would be funded with a combination of debt and equity, with about 25 per cent of the enterprise value coming from selling shares to existing investors.

Shares of Bayer dropped to their lowest in more than 21/2 years.

The proposal gives investors insights into chief executive officer Werner Baumann's style and ambitions as he attempts to pull off the biggest-ever corporate takeover by a German company after less than a month at the helm.

The two companies are engaged in "constructive discussions", the CEO said.

Buying US company Monsanto would give Bayer the world's largest seed supplier and a pioneer of crop biotechnology.

The kind of genetically modified seeds that Monsanto started to sell two decades ago now account for the majority of corn and soya beans grown in the United States

Bayer fell 3.4 per cent to €86.48, the lowest since October 2013, as of 9.07 am in Frankfurt trading.

Bayer's stock had plunged by the most in seven years when it confirmed having made an offer, without disclosing the financial details, last Thursday.

Monsanto has not responded to the offer publicly, beyond saying that it was reviewing the terms.

"What we saw last week was an uneducated reaction in the media and the press because we did not communicate the details of our proposal," Mr Baumann said in a conference call yesterday. "We are utterly convinced of the rationale" of the proposal, he added.

The deal will add to core earnings per share by a mid-single-digit percentage in the first full year after completion, and a double-digit percentage thereafter, Bayer said.

The German company also expects earnings to be bolstered by savings of about US$1.5 billion from the fourth year following the deal.

The offer marks a reversal of roles for Monsanto. The company previously sought to buy Swiss pesticide maker Syngenta, but had to abandon the US$43.7 billion bid in August after the other company refused to agree to a deal.

The crop and seed industry is being reshaped by a series of large transactions.

China National Chemical Corp agreed in February to acquire Syngenta for about US$43 billion, months after Monsanto abandoned its own bid.

Meanwhile, DuPont and Dow Chemical plan to merge and then carve out a new crop science unit.

Bank of America Corp and Credit Suisse Group are the financing banks for Bayer, while Rothschild has been retained as an additional financial adviser.

BLOOMBERG