This study is concerned primarily with sclerenchymatous idioblasts. These idioblasts are polymorphic, and are commonly termed sclereids. The term sclereid is derived from the Greek work skleros (meaning hard). The hardness of sclereids and sclerenchyma tissue is due to their thickened cell walls, which are for the most part lignified. Their principal function is mechanical giving strength to plant tissue organs, therefore, enabling them to withstand various environmental stresses. This paper deals with the foliar sclereid type of sclerenchymatous idioblast. The study of sclereids raises many of the fundamental problems of botany. Some of these are: growth and development, senescence of cells, intercellular relationships, and the value of idioblastic cells in systematic taxonomy. This study is not an attempt to answer all of these problems, but it is presented in the hope that it may give some additional information toward the solution of some of these fundamental problems.