The 10 million dollar project was funded entirely with private money. From a press release:
When the National Garden opens to the public on October 1, 2006, it will mark the successful completion of one of the first public-private projects undertaken by the Office of the Architect of the Capitol. The project was solely funded by private donations raised by The National Fund for the U.S. Botanic Garden.
This not-for-profit corporation raised $11.5 million in private contributions pursuant to Public Law 102-229. The National Garden’s mission is to educate visitors about the great diversity of American plants and their importance to the environment; to help connect people to nature; and to demonstrate the relationships between plants, water, and humans.
As you can see the designers have created several different rooms each with their own separate type functions. It appears this will allow visitors to have many unique experiences as they work there way
through the gardens. I look forward to visiting