She was long gone, but she came to him in a dream.

Artist John E. Dowell Jr., 77, Philadelphia born and bred, said it all came down to Big Mommy.

"I had this dream, a series of dreams, three months before I had a show in Savannah back in 2011," Dowell said the other day while standing in the midst of his extraordinary new exhibition, Cotton: The Soft, Dangerous Beauty of the Past. 

The exhibition of vivid photographs of cotton plants, cotton fields, and the ghosts of cotton, many collaged and profoundly manipulated, just opened at the African American Museum in Philadelphia, Seventh and Arch Streets. It runs through Jan. 21.

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"I kept dreaming of my grandmother and so I kept asking my brother and my sister, 'Did you dream of Big Mommy?' And they said, 'No.' And finally my sister said, 'You're in trouble.' I said, 'But I haven't done anything!'

"She said, 'Big Mommy don't play! You know that. She never played!'"

Dowell, a slight man with a sparkling laugh, said that, about two or three weeks later,  he had another dream.

"I said, 'OK, Big Mommy, what did I do? What's wrong?" he recalled. "And I saw this image of her with cotton and I started remembering the story she told me about cotton."

Big Mommy, who grew up near Augusta, Ga., told a memorable tale of children — and herself — becoming lost in fields of towering stalks of cotton, cotton looming, cotton everywhere, as thick as any endless, foreboding woods.

"The next morning," Dowell continued, "I called a farm agent in the Savannah area and I found a farmer and made an appointment for when I was going to go down to the [Savannah] museum."

So began Dowell's journey into what was the alien world of cotton, seemingly so antithetical to his urban own world of the Richard Allen Homes and decades of teaching at Temple's Tyler School of Art. But he felt in his bones the vast power and terrible beauty of this potent plant, and understood that he had to know cotton, as an artist and a photographer — and perhaps most profoundly as a black man.

"Cotton is our symbol," Dowell said. "That's black people in this country. You just mention cotton, you know what I mean, and for those of us who are a little aware, all the torture, all of that stuff — it's there. And it makes you stop and think. That's why I'm doing the cotton. I couldn't think of a better symbol."

In the midst of his first visit shooting near Augusta, the farmer who showed him around proudly told Dowell that the cotton fields had been in his family for seven generations.

"It hit me — I've been taken home," Dowell said. "I didn't trace it, but I could feel it. I knew somebody in my family worked that property. I didn't let on. I just went off and tried to photograph. On the second day, I'm photographing in the afternoon, and all of a sudden, I can't focus. I'm a nut about focus. I said, 'What's wrong?' All of a sudden, my eyes started watering and I just cried. I just cried. After a while I got myself back together. … That was my first real experience of cotton."

Photographing that year, mostly in Virginia and South Carolina, Dowell said things, powerful things "would happen." Once, driving to an obscure field, he turned a corner, came over a hill, and "all I can see is solid cotton."

He pulled over.

"I just sat there," he said. "I thought, 'Man, what are you going to do if you face all of that at 5 in the morning for the rest of your life?' Things like that I had never thought about before."

Some things, as his exploration of cotton continued, Dowell had never even heard of, particularly when he began thinking about slavery in the north. The Wall Street slave market, for instance, was one of world's most active selling blocks for most of the 17th and 18th centuries.

But by the 1820s, freed Africans were able to buy plots of land in what became known as Seneca Village, a largely black community in what is now Central Park. From 1825, blacks and some Irish and German families bought land there and built homes.

The city swept it all away with the power of eminent domain to create Central Park. Nothing remains visible of Seneca Village, not the houses, the three churches, the school, the businesses.

Dowell photographed the area and in some of his most powerful prints, he drew buildings on their exact sites, ghost houses and cotton haunting the park.

There is the home of Andrew Williams, for instance, the first settler, who bought his land and built his simple house in 1825.

In Dowell's photograph, he shows the spectral Williams house surrounded by vivid cardinals, "spirits," Dowell calls them.

Another print shows the house of Williams' neighbors, levitating. Nearby, the African Union Church sits, cotton laid at its doorstep, bursts of cotton flying from its rooftop, an explosion of hallelujahs.

"I wanted to show the spiritual," Dowell said. The same idea inspired his interior shot of Trinity Church near Wall Street, which sometimes allowed black people to be buried in its cemetery, and often barred them.

Cotton pokes its way above pews in Dowell's photographic vision; it comes streaming through the windows like angels in Renaissance paintings.

"I superimposed cotton on [the interior]," he said. "But what it's about is that, OK, we're just equal like everybody else, you know, nothing special. Just give us a shot like everybody else. The message is: You could bury us. You could. I just want people to remember and to think about what happened there.

"My job is to plant a little seed. But I'm still trying to make pictures. I want the feeling. … People ask me, 'What are you trying to do?' I'm trying to show you what you can't see."