The motto of Minnesota's MacMillan family, heirs to the Cargill fortune, could be that the only good mouth is a closed one - unless it happens to be eating a grain-based food product.

One of Minnesota's wealthiest clans, the MacMillans also have been one of its most doggedly secretive. But the recent publication W. Duncan Macmillan of Wayzata, offers the closest look yet at the private lives behind the largest privately held company in the world.

Anyone hoping for a scandal-laced tell-all will be sorely disappointed. In fact, sensational or otherwise, information on the current activities of any Macmillans still living is scant. Whitney MacMillan , Duncan's cousin, is generally credited with running Cargill very well in the 1970s through mid-1995, when the company realized much of its growth.

This book primarily paints portraits of Duncan's grandfather, John Hugh MacMillan , and father, John H. MacMillan Jr., who were the most instrumental figures in shaping what today is a $51 billion Cargill business, and laying the groundwork for the company's status as a dominant player in the international food market and diversification into finance and other business arenas.

As portrayed in the book - published by the MacMillan -bankrolled Afton Historical Press - both men were the right leaders at the right time. John Sr. was a cautious, by-the-numbers type who revived a company foundering from the depression of the 1890s, and John Jr. was a relatively bold, experimental type whose instincts brought further expansion in the growth boom of the 1950s.

Even though Duncan MacMillan can afford to throw things away, he "never much liked to," he said in a recent interview at his home in Wayzata. Excerpts from his collection of family letters comprise the most interesting and revealing inclusions in the book.

Today, no MacMillans are active in the company's day-to-day operations, although several sit on its board. Neither Duncan nor his older brother John Hugh III, who lives in Florida, ever emerged as key leaders of Cargill. Those roles were filled by his cousins Whitney MacMillan , who ran the family business for nearly 20 years before retiring in 1995, and his brother, Cargill MacMillan Jr. With an estimated personal worth of $975 million each, the three heirs are tied for the position of 5th richest Minnesotan, according to Forbes magazine.

"I don't think the rest of the senior members of the family are all too happy about the book. I didn't ask. The younger generation is OK with it," he said.

None of Duncan's four daughters live in Minnesota, but they were in town recently for a company shareholders' meeting.

For Alexandra Daitch, the youngest at 36, the book "really reconfirmed what great and different thinkers my grandfather and great-grandfather were - the first focused on grades and performance, the second on personality and character - and how right for their respective times both of their management styles were."

Her sister, Katherine, 44, said the book made her feel "proud of her heritage, to know that I was raised under that roof. The knowledge of the past helps to improve the knowledge and the lives of the future generations."

The rest of the MacMillans remain as mum as ever where public comment is concerned. When reached by telephone at his home between an Arctic fishing expedition and a visit to his Colorado retreat, Cargill MacMillan Jr. said he had not yet read the book, so he couldn't comment. None of the other family members returned calls.

Charmed life

Duncan, 68, has a reputation as a more eccentric, at times flamboyant, personality than his cousins. An avid athlete, he currently is best known as the owner of Rush Creek Golf Course, where he was instrumental in attracting last weekend's LPGA tournament.

Duncan's Cargill career began with cleaning generators as a youth. From the mid-'50s to the mid-'60s, he oversaw European trading for eight years, based in Geneva, then came back to Minnesota to run Waycrosse, formerly Cargill Securities Co., which had been set up as a trust to protect the company's assets. In the 1970s, he was instrumental in steering the company toward its steel interests. From 1966 through 1997 he served on the board of directors, and he is now a director emeritus.

Duncan spends his time playing golf, raising orchids, puttering with his ham radio in the basement and getting his captain's license so he can pilot his yacht in Florida, where he also maintains a home. In September 1996, he married Nivin Snyder, 55, also of Wayzata.

While his two-story house could be called typical of the upper middle class, it does not look like the castle a man of his wealth might erect. And with characteristic MacMillan frugality, his sartorial style is more "fall into The Gap" than ascots and driving gloves.

"Nivin tells me I dress like a farmer," he said, giving his wife a poke in the arm. "I tell her, well, that's really what I am."

MacMillan 's philanthropic contributions have been funneled primarily into causes and institutions about which he is passionate - medicine and his alma mater, most notably. He and his late wife Sarah (Sally) MacMillan donated $1.1 million to the Minneapolis Children's Medical Center in 1993 to build its pediatric intensive-care unit, and over the years Duncan has donated nearly $20 million to Brown University, where he has funded a science center and gym facilities and endowed a number of chairs in liberal arts.

MacMillan calls his relationship with Brown "one of the most important commitments of my life." "He has 3 B's and a C for his midterm, which in the history of our branch of the MacMillan family is something unparalleled."

Sally, who died of cancer three years ago at the age of 63, was an avid gardener. In her memory, Duncan has contributed a new terrace being built at the University of Minnesota Arboretum in Chanhassen.

But considering their prominence in the Minnesota business arena, the family has a much lower profile than the likes of the Daytons and the Pillsburys.

In Duncan MacMillan 's view, his family's downplayed community presence parallels that of Cargill's familiarity to the general public.

"We don't sell products that go into people's mouths or on their bodies," he said. "We sell to the people who sell them."

Life with father

The Cargill/MacMillan union formally began when John Hugh MacMillan Sr. and Edna Cargill were married in 1895 in La Crosse, Wis., where both families were then based. Control of the business shifted from the Cargill to the MacMillan side of the family in 1907, a few years after the move to Minneapolis and the death of patriarch Will Cargill.

John Jr., Duncan's father, was born in 1895. Duncan remembers his father as an aggressive personality who cut his own hair because he didn't like to be touched and was so competitive that he would profess to having excelled at sports that didn't exist in his youth, such as water-skiing. An early proponent of healthful eating, he held that a radical 1950s diet of rice and fruit juice saved his life, and eschewed salt long before it was fashionable.

MacMillan described his parents' style of child-rearing as "Victorian. There was a distance between us and them. In today's world there's more of an exchange in the relationship. I can't say one is better than the other - it's just different."

The property his grandfather bought in what is now Orono was split among the MacMillan families. The Whitney boys, including Wheelock Jr., lived across the street, and were practically family as well. The boys roamed in packs, going to breakfast clad in their hockey clothes in the winter and playing baseball, kick-the-can and hide-and-seek in the woods in the summer.

back-yard circus and had a real flaming hoop rigged up that we were shooting through on our bicycles. Grandpa came out and put a stop to that."

One of the craziest stunts MacMillan cooked up as a teenager was playing Jacques Cousteau with his best friend David Bell, whose family founded General Mills. According to Duncan, the two put on some diving suits, the "heavy old kind that if you fell over in them you couldn't get up," and walked themselves across the bottom of Lake Minnetonka, breathing through rubber tubes attached to a homemade air tank set up on an unmanned boat above them.

Bell, a Marine pilot during the Korean War, died in 1955 when his plane crashed in fog over the Sea of Japan.

Keeping focused

MacMillan said the most important lessons he learned from his father were "discipline and honesty. And sacrifice - the corporation came first. From my mother, it was social skills - an area in which I have a lot of talent."

To outsiders, however, it seems that the most important lesson that all MacMillans have learned is to keep their affairs, both personal and professional, to themselves. While past and present generations of the family have had their share of the kind of problems no family wants to broadcast (such as drug and alcohol addiction), their obsession with privacy is all-encompassing.

"The grain-business philosophy of being close-mouthed goes back to the ancient Greeks," Duncan said. "When a fellow going into port had more cargo than he sold and other people found out about it, the market would collapse. So they tended to be that way about their whole lives, not just inventories and stocks."

"My grandfather hated getting his name in the paper. Time magazine once printed an article criticizing the company, and his way of commenting was to call up and cancel his subscription. . . . We don't talk about the family, period."

"In order to survive the tremendous upheaval of booms and busts, you have to be patient. A farmer will never admit to having a good year or a bad year, no matter how profitable or grim it gets; he'll always say things are solid. No matter who asks, he's not going to talk about it. I guess we inherited that."

Duncan's book might be the most personal history of the family to which the public will ever have access. And his role as family historian might be what he himself is most remembered for.