Works of art often last forever, or nearly so. But exhibitions themselves, especially gallery exhibitions, are like flowers; they bloom and then they die, then exist only as memories, or pressed in magazines and books.

This quote is stating that artwork often endures for a long time, but physical exhibitions such as in a gallery will not. They will be displayed for a certain period of time and then afterwards will only exist as photographs, records or stories. The physical exhibition will cease to exist even though its memory might remain.