Which layer of a root or stem is located immediately under the epidermis and outside the endodermis?

The layer located immediately under the epidermis and outside the endodermis is the cortex. The cortex in plant roots and stems is a fundamental tissue structure, primarily composed of parenchyma cells, which play a role in storage and transportation of nutrients and water. In roots, the cortex serves as a barrier to prevent pathogens from entering the vascular system and also aids in the transport of water and nutrients from the soil.

The vascular cambium, on the other hand, is involved in the growth of vascular tissues (xylem and phloem) but is situated deeper than the cortex. It is not immediately beneath the epidermis. The pericycle is the layer that lies just inside the endodermis, playing a role in lateral root development, which also places it deeper than the cortical layer. Primary tissue encompasses all the tissues developed from the apical meristem; while it includes the cortex, it is a broader classification that does not specify the exact placement in relation to the epidermis and endodermis.

Thus, the cortex is the precise answer as it is located directly beneath the epidermis and outside the endodermis in both roots and stems.