Nyffeler R., Eggli U., Leuenberger B. E., Noteworthy idioblastic sclereids in the stems of Eulychnia (Cactaceae), American Journal of Botany, 1997, 84(9):1192-1197, doi: 10.2307/2446042
The abstract describes two types of lignified sclereids in the cortex and pith of stems from nine Eulychnia accessions. Elongated cells in the outer cortical layer are perpendicular to the stem surface, while inner cells are spherical or nearly spherical. It discusses secondary wall development and the diagnostic value of these structures. A reinforcing function is the authors' assumption.