On the macro-chemistry of the endodermis

As our knowledge of the processes of development in the plant body grows in precision, increasing importance attaches to that detailed knowledge of the structure of a tissue system which enables a more correct assessment of its influence upon the growth and development of neighbouring tissues. This is particularly true of that cylinder, one cell in thickness, which is known as the endodermis, which is almost invariably present in the root of a vascular plant, and very frequently found also in the shoot (4). This cylinder passes through a series of developmental stages, and micro-chemical tests indicate that the structural features of these different stages are very distinct. When the cells of the endodermis cease to be meristematic, as they are left behind the growing point, the cell protoplasts of this layer remain embedded in the walls of each cell in the region of the Casparian strip. This strip is continuous around the radial longitudinal and transverse walls of every cell, so that the result is to make this cylinder, one cell in thickness, a cylinder in which the Casparian strip may be visualized as a network, with the meshes in the network completely filled by the living protoplasts. The protoplasts at this stage are very definitely semi-permeable. Within the endodermis are the vascular elements; these contain water and water-soluble substances, which are able to leak out along the cellulose walls of the cells which surround the vascular channels.