But one program at the museum has continued its daily tradition of laying out a white rose for each person killed in both the 2001 and 1993 terrorist attacks whose birthdays would have been celebrated that day.

Since 2013, museum employees have placed the flowers on the inscribed names of those memorialized at the fountain.

Museum officials have continued the Birthday Rose program during the closure because “we felt it was core to our mission and would be a ray of light during this intensely difficult time,” Kate Monaghan Connolly, a museum spokeswoman, said.

Visitor services staff members typically placed the flowers daily. But with them no longer working, the task is now carried out by security and operations workers, who are classified as essential employees.

The flowers have long been donated by Floratech, a TriBeCa florist, whose owner, Michael Collarone, shut the shop because of the statewide order to close nonessential businesses.

But Mr. Collarone, known widely as Mikey Flowers, said he was determined to keep supplying the roses “so we could have some continuity and normality in the city right now.” With his local distributor also shut, he has been ordering the flowers from a supplier in the Netherlands.

“I want to show people that the world is not over,” said Mr. Collarone, who was in Lower Manhattan during both World Trade Center attacks. “We are going to get past this together.”