The external surfaces of pear sclereids commonly are illustrated as covered with apertures. This SEAA investigation of the surface features has shown the surface to have few or no apertures. When the primary wall layer was removed the typical ramiform canal system was obvious. This observation confirms the often-ignored fact that the pitapertures of the secondary wall are not continuous with the primary wall. Hence, they do not show on the surfaces of the intact cell.
Sinclair, Clarence B.
"Scanning Electron Microscope Study of Brachysclereids of Pear (Pyrus communis L.),"
Journal of the Arkansas Academy of Science: Vol. 30
, Article 31.
Available at: http://scholarworks.uark.edu/jaas/vol30/iss1/31