Of course, images speak their own language. And Morris did a book in 2010 called Always Growing that tells the arboretum's story in words.
That story began in 1886, when John Morris, a millionaire iron manufacturer, and his sister, Lydia, bought 26 acres here to build a country home. From the beginning, they envisioned that their private estate would become a public garden - and, in 1933, it did.
But most of the transformation has taken place over the last 35 years, with guidance from a master plan and, to a large extent, Meyer, who was hired as horticulture director in 1976.
Since then, the garden has evolved, in his words, "from a state of tattered elegance" to a nationally known arboretum.
Today it encompasses 166 acres, including the planted landscapes on the Philadelphia side of Northwestern Avenue and Bloomfield Farm on the Springfield Township, Montgomery County, side. The arboretum has been affiliated with Penn since 1932, and was designated Pennsylvania's official arboretum in 1988.
But that doesn't tell Morris' story as Meyer has lived it. And he has lived it, not just as a horticulturist and globetrotting plant collector or even amateur photographer. He and his wife, Debbie Rodgers, a risk manager at Aramark, actually live there, in an old farmhouse built by the Morrises on Northwestern Avenue.
This has blurred the distinction between home and office, which, as anyone who works at home knows, can be problematic. But Meyer seems to have used his director-without-borders existence to advantage.
He carries a camera everywhere, whether touring the garden's historic trees with donors, counting heads at the popular "Out on a Limb" canopy walk, or walking leisurely with his wife.
(Meyer uses a Nikon D7000 single-lens-reflex digital camera, and a pocket-sized Panasonic Lumix. Both have accompanied him on plant expeditions, most recently to the Chinese provinces of Shaanxi and Gansu last fall.)
"Because I live here, I could be out having a drink at the end of the day on my back terrace and all of a sudden I'll think, 'Oh, look at the light!', and run inside and pull my camera out," he says.
Inspiration also strikes on Sunday mornings, when he and Rodgers like to stroll through the arboretum - "to my wife's annoyance," Meyer says, laughing. "As soon as I pause to take a picture, she does her power walk. Off she goes."
The book's cover shot presented itself at 5:30 a.m. around the summer solstice one year, when Meyer accompanied a Better Homes and Gardens photographer who wanted to shoot the Rose Garden. The photographer's work never appeared in the magazine, but Meyer's became a book cover:
Soft yellow sunlight streams through the trees into a lovely tumble of red, white, and pink roses, lavender foxgloves, and catmint. The grass is a delicious green, offsetting the rainbow of blooms, which brings to mind a story from the Morris era - how every morning in spring and early summer, a beautiful bouquet of roses was gathered here, thorns carefully removed, and walked up to the house.
It's the kind of image that instantly lowers blood pressure. It also illustrates the importance of light in photos, especially of gardens, which are by nature highly ephemeral.
"More and more I've come to realize that a great photo is not what you're taking a picture of. It's how the light is hitting it," says Meyer, who takes pictures to illustrate his horticultural lectures and articles, as well as Morris' newsletters and publications.
Light is most interesting in early morning and evening, and that is when many of the images for Meyer's book were snapped. He took more than 30,000, which he winnowed down to 500 and handed over to a six-member committee. They chose the final 100.
Besides the Rose Garden, another popular spot included in the book is the Swan Pond, inspired by the romantic English landscapes of the 18th century. It was created in 1905 by damming up a brook that runs through the arboretum.
The photo captures the scene about 9:30 one winter morning. The sun is low; the water dark; the snow and swan, pure white.
Meyer has his own favorite. He turns to the book's back cover; it's the north-facing Magnolia Slope, by the visitor center.
"I have hundreds of shots looking down this hillside," he says.
He took this one at sunset. The Wissahickon Valley is framed by trees, trees everywhere. "It's an incredible band of green, a little like a kingdom," Meyer says.
He describes the natural constituency of his book, which costs $39.99 at the Morris gift shop and Penn bookstore, as "Morris people" - members, visitors, supporters.
Beyond that, it's intended to create a historical record. "I hope 50 years from now, people will look at this book and see how things have changed," he says. "I hope they say, 'Look how much better we are today.' "
Read gardening writer Virginia A. Smith's blog at www.philly.com/ginny
VIDEO: Paul Meyer, Morris Arboretum director, discusses the key to garden photography: changing light. www.philly.com/ginny
Contact garden writer Virginia A. Smith at 215-854-5720, email@example.com, or @inkygardener on Twitter.