About 30 species of Elderberry make up the genus Sambucus of the family Caprifoliaceae. A lenticel is a loose aggregation of cells that penetrate the surface of a woody plant. Upon close inspection, it appears to be a blister-like break in the surface. These cells exchange gases between the atmosphere and the underlying tissues. Each lenticel becomes a pathway through which oxygen and other gases can diffuse to the living cells of the bark. Without sufficient oxygen, the cells of bark would die.