its vascular cylinder is only partly advanced. In gymnosperms and angiosperms displaying secondary growth, the roots commonly develop only endodermis with Casparian strips. In many of those, the endodermis is later discarded, together with the cortex, when the periderm develops from the pericycle. If the pericycle is superficial and the cortex is retained, either the endodermis is stretched or crushed or it keeps pace with the expansion of the vascular cylinder by radial anticlinal divisions, and the new walls develop Casparian strips in continuity with the old ones. In the absence of secondary growth (most monocotyledons and a few eudicots), the endodermis commonly undergoes wall modifications. There are two developmental stages beyond the development of the Casparian strip. In the second stage suberin (or endoderm) coats the entire wall on the inside of the cell. As a result, the Casparian strip is separated from the cytoplasm and the connection between the two ceases to be evident. In the third stage, a thick cellulose layer is deposited over the suberin, sometimes mainly on the inner tangential walls. The thickened wall, as well as the original wall in which the Casparian strip is located, may become lignified, creating a secondary cell wall. The Casparian strip may be identifiable after the thickening of the endodermal wall has occurred. The thickened endodermal wall may have pits. The successive development of endodermal walls is clearly expressed in monocotyledons. Discovery The discovery of the Casparian strip dates back to the mid-19th century, and advances in the understanding of the Endodermis of the root of plants. In 1865, the German botanist Robert Caspary first described the endodermis of the root of plants, found that its cell wall was thickened, and named it Schuchtzscheide. Later scholars called the thickened part of it the Carls Belt, which was named after Casbury. The term "Caspary'schen fleck"（） appeared in the 1870s literature, and after the 20th century, it was often called the Casparian strip. In 1922, researchers first left the Casparian strip from the root of plants to study its composition. Composition The chemical composition of the Casparian strip has been controversial for a long time. Casbury pointed out that this structure may be composed of lignin or suberin. Later scholars mostly thought it was suberin. It was not until the 1990s that after analyzing the Casparian strip of several plants, it was found that lignin was the main component, but