Plant tuber
A plant tuber is a fleshy, thickened storage organ of plants that grows underground. The plant tubers used in agriculture are also called tuber vegetables or tuber fruits , although they are not fruits in the botanical sense. Plant tubers are metamorphoses of the basic plant organs, stem ( stem ) or root (tuber). The tuber serves the plants to store reserve substances and to survive unfavorable living conditions such as winter or drought. In contrast to tubers, onions are metamorphoses of the stem and leaves, with the transformed leaves taking over the storage function. The best-known tubers are the edible sprout tubers of the potato . Tuberous roots are found in cassava , dahlias , celandine , yacon .
In legumes , nodule bacteria live in thickened roots. However, these nodules are not nodules in the sense discussed here.
Root tuber anatomy
Root tubers show the typical structure of the cormophyte root ; the central cylinder surrounded by a secondary endodermis with pericyclic , xylem and phloem cords and surrounding cortical layer . In the tuber, this bark layer is transformed into a large-cell starch storage parenchyma through the storage of many comparatively large amyloplasts . The differentiation of the amyloplasts in the formation zone of the storage parenchyma around the central cylinder is also shown.