He is a doctor whose pioneering research and development work helped to eliminate an infectious disease that once struck thousands of children each year. She is a four-decade resident of the Vineyard and a pioneer in her own right, an avant garde horticulturalist whose work in her North Tisbury arboretum has received national recognition.
Today David H. Smith and Polly Hill are partners in a project that is unique among conservation efforts on the Island. Theirs is a rare alliance, born in part of the providential bits and pieces which sometimes bring two people together. 
On an early August day, Dr. Smith sits in a chair on one of the many grassy paths that ramble around Polly Hill’s magnificent arboretum. A short distance away the tall ferns of an ample asparagus bed wave in the late summer breeze. The asparagus patch is wrapped in a wide border of raspberries. Seated in the shade of a towering stand of her famous Stewartia trees (all grown from seed, like everything else on the property), Dr. Smith waves away a question about the delicate pink flowers poking above a ground cover nearby.
“I don’t know what anything is,” he smiles. “You have to ask Polly.”
At the moment Mrs. Hill, who is 90, is showing a visitor around the property in her trademark golf cart.
Never mind the names of the plants, Dr. Smith knows the value of Barnard’s Inn Farm, the unique 60-acre farm that has been Polly Hill’s horticultural laboratory for the last 40 years.
Early last month it was announced that the farm will be permanently protected through a purchase by the Polly Hill Arboretum Inc., whose founder and chairman is Dr. Smith.
This unusual partnership began a couple of years ago when Dr. Smith, who has been coming to the Vineyard as a seasonal resident for nine years, began to take an interest in conservation.
He paid a visit to the Mary P. Wakeman Center and met with the various Island conservation groups that are housed there.
“I began to talk to people about what is available and what is important,” he says during a rare newspaper interview. “And someone asked, ‘Do you know about the Polly Hill property.’”
He did, because his wife is an avid gardener. “This is my wife’s favorite place on the Island, and when we found out that it wasn’t being protected, we said, whoa, you can’t let that happen.”
It was a new challenge for Dr. Smith, a pediatrician with a preeminent career in academic medicine who earned national recognition in the late 1980s for his role in developing a vaccine against childhood meningitis, a disease which at one time struck some 20,000 children annually. The vaccine eventually eliminated the disease, and Dr. Smith’s work is the basis for widespread research under way today in developing other vaccines against bacterial childhood infections.
Dr. Smith received the prestigious Albert Lasker Award for his work last year. 
Today he is a quiet and solitary benefactor who shuns public attention, speaking only reluctantly about his own career and background. Among other things, he grew up in Ohio and was later trained in the Harvard University system, eventually leaving Harvard to pursue his medical research at the University of Rochester. He later left medical research and started his own private foundation in New York city.
And his current passion is the Polly Hill story.
“It’s a fantastically inspiring story,” he says. “You can’t spend any time with Polly and not get really excited about what she does.”
Beginning in 1957, Polly Hill, who was then 50 years old, began her gardening experiments on what was originally the Smith sheep farm in North Tisbury. The mother of three and the wife of Julian Hill, a chemical engineer at DuPont who was known for his role in the invention of nylon, Polly employed the training she had obtained at Longwood Gardens, Winterthur, and the University of Delaware.
And at age 50 she embarked on a 40-year career of amateur gardening that would rock the horticulture world. Her mission was to evaluate the best plants and trees to grow on the Vineyard, and she grew everything from seed. Julian Hill’s work took him around the world and Polly traveled with him, collecting seeds that she later used in her experiments.
Today, more than 2,000 plants and trees are displayed around large meadows in her own unique rural landscape design. There are camellias and towering magnolias which no one ever knew could grow north of the Mason-Dixon line. There are also hardy hollies, conifers and rhododendrons. She introduced more than 100 species, including a family of 22 North Tisbury azaleas — low-growing, late blooming, hardy plants, all named after her children and grandchildren. 
“Here is a woman who had never gardened at all until she was 50 years old and she basically began as an experimenter. She is a researcher and she is a risk-taker. If you want to start over again, Polly is the model,” Dr. Smith says.
Her work shattered the notion of zonal gardening, which is based on the premise that certain plants grow only in certain climates. Dr. Smith says: “What we are seeing in its most native form, she has done genetic engineering. She has stressed the genetic system to render its full potential.”
Is this marriage of science and conservation unusual? Dr. Smith doesn’t think so.
“I don’t think I’d be here if I were an accountant,” he says. “Polly has taken amateur horticulture to a new, higher level. She kept tremendous records, about what worked and didn’t work. I’ve been going to seminars at the National Science Foundation for a long time, and I think I can say with some authority that she’s got some secrets here.”
He also said: “I believe very strongly in mentoring and I think it is an important aspect of why we end up where we end up. Polly Hill is not only smart and committed, she’s tough. I think people who know the garden know about its unique qualities — and everybody talks about the serenity of the place.”
The arboretum will be closed to the public for a year for inventories and planning, but Dr. Smith said future plans include educational programs for all ages and a summer institute for horticulturalists. He sees the farm as a place where art and horticulture could be combined, for example, through classes in watercolor painting. The challenge is to create public use and still preserve the rural environment — and continue the plant research.
For Dr. Smith, protecting the Vineyard is a top priority.
“I have done a lot of thinking and it seemed to me that conservation is one area I could do something,” he says. “Not only will conservation improve the quality of life here, but now the question is whether there is going to be the leadership, whether the townspeople will pick up the baton and run with it.
“And the message, a clarion call for the whole thing, is that economically it makes so much sense. There have been six to eight studies done, and the results are the same, which is that for every dollar brought in by taxes, if the property is residential, it costs $1.40, if it is commercial, it costs 80 cents and if it is in conservation it costs 40 cents. So why don’t we just get on with it?”