Zachariah Deminieu Blackistone Sr., 111, the founder of Blackistone Florists Inc. and a man who provided young and old alike with a notable example of industry, vigor and grace, died Sunday at the Bethesda Retirement and Nursing home. He had pneumonia.

Mr. Blackistone was a descendant of a family that arrived with the first English settlers in St. Mary's County, Md., aboard "The Dove" in 1634. He was born at Charlotte Hall. When he was still a youth, his mother urged him to take a riverboat to Washington and seek his fortune working for the government.

Instead, he came upon the Madame de Wattville. That was a rose, and Mr. Blackistone found it at the old Central Market at Seventh Street and Pennsylvania Avenue NW, the present site of the National Archives, where he had gone to look for work.

"A white rose with a deep pink blush on the petals," he said in describing the Madame de Wattville some 70 years later. "I was so overcome and enthralled by the beauty of these flowers that I decided right on the spot that I wanted to be a florist."

In 1898, with $10, he rented a store on F Street near H Street NW. Shortly thereafter he expanded to a location at 1407 H St. NW, where the business remains. There are branches in the Spring Valley section of the city and in Bethesda and Rockville. Mr. Blackistone worked seven days a week, except when he was out of town, until 1976, when he moved to the Bethesda Retirement and Nursing Home. He kept in touch with the firm until his death.

Over the years, Mr. Blackistone came to know many of the great and the near great and saw many a memorable event. In 1906, for example, he was there when President Theodore Roosevelt laid the cornerstone of the Washington Cathedral. One of his daily customers was "Uncle Joe" Cannon, Joseph Gurney Cannon, the redoubtable speaker of the House of Representatives. Mr. Cannon used to stop on his way to Capitol Hill for a boutonniere.

Some things never seemed to vary. One was Mr. Blackistone's daily schedule. He arose at 5:30, ate breakfast, said his prayers and was in his main store by 8. He stayed there until 6, lunching on a sandwich and a glass of buttermilk. In his 80s, he would take a short nap in the afternoon.

Apart from daily jogging and other exercises, he played golf and took part in a tournament at the age of 100.

Another thing that never changed was Mr. Blackistone's feeling for flowers and his notion that they should be available to everyone.

"The sentiment of flowers is what makes them unique," he said in an interview with The Washington Post in 1952. "They say more and mean more than anything else in the world."

When Mr. Blackistone started his business, the area around 14th Street was "uptown" Washington and largely residential. He attributed his early success to this location. Much trade came to his door in carriages--it was, in fact, the carriage trade. It was not long before his enterprise was on a sound footing.

"First sale I ever made was a single La France rose for 25 cents," he recalled in his 88th year. "At that time 25 cents for a rose seemed so impossible when I compared it with a bushel of potatoes I used to dig in the country and sell for 50 cents that my conscience hurt me all night."

Years later, Mr. Blackistone started the Cash and Carry Flower Shop, where, he said, "a customer who has only 25 cents will always be welcomed and find something he can take home to a sick wife or to add a touch of beauty to the family weekend."

Mr. Blackistone, who was known as "Zeddie" in the trade, contended that the continued growth of the flower industry was attributable to the use of telegraphic orders and the slogan, "Say It With Flowers." In the 1930s, he himself introduced "the goodwill dozen." This was 15 roses for the price of 12. "They make for a better display, a good value, and I want the traffic," he said. At his death, he was the oldest member of Florists Transworld Delivery (FTD) and a life member of Allied Florists of Washington. He was a member of Kiwanis International, the Masons and the Kenwood Golf and Country Club. He was senior vice president of the Oldest Inhabitants of Washington.

His wife, Sara Virginia, died in 1956. Survivors include a son, Z. D. Blackistone Jr., of Chevy Chase; two daughters, Margaret Blackistone of Crofton, Md., and Virginia Milburn of Sherwood Forest, Md., five grandchildren, and six great-grandchildren.