In this article we will discuss about the functions of storage organs of beta vulgaris, explained with the help of suitable diagrams.
Biennials, besides seeds, have fleshy and swollen root or stem that store nutrients. The biennial herbs store nutrients in the first year. This is for the development of the flowering shoot in the following year. Many important food plants have storage organs.
The anatomy of all storage organs has the following common features:
(1) Normal or accessory cambia cause the thickening of the storage organs. It is to note that formation of accessory cambia is a taxonomic character that is inherited by a species. Formation of accessory cambia is not an adaptation to a specific function. The dilatation of cambial rays and the proliferation of other parenchyma may fortify the thickening.
(2) Tracheary elements are poorly developed. Comparatively phloem elements are well developed.
(3) Parenchyma cells are the storage tissues in storage organs. They are thin-walled and formed profusely in various ways.
Ample development of parenchyma cells that store nutrients, ample development of sieve elements through which large transport of organic compounds occur and rapid development of the storage organ can be accomplished in various ways. One of the methods is illustrated below on the basis of anatomy of the storage root of Beta vulgaris (Fig. 29.17).
Diagrammatic illustrations (A-C) of storage tissue formation in Beta vulgaris.
Anatomically mature root of Beta vulgaris shows peripheral periderm consisting of phellem, phellogen and phelloderm, a few layered parenchymatous cortex below periderm and stele.
The stele comprises proliferated pericycle and five to eight concentric rings of growth layers. Accessory cambium, vascular tissues and parenchyma present between vascular tissues compose each growth layer. Between the growth-layers there occur parenchyma tissues.
Primary stele of the root is radial with diarch xylem. At the time of secondary growth a regular cambium is formed. Phellogen originates on the peripheral side and forms periderm. Periderm covers the surface of root and forms a protective layer. Pericycle proliferates. Parenchyma originates between periderm and stele.
Later five to eight accessory cambia originate in succession outwards. These cambia divide almost simultaneously. The derivative cells differentiate into narrow strands of vascular tissues and parenchyma. Broad cambial rays separate the narrow vascular strands. Tracheary elements are weakly differentiated.
The vascular strands are mainly composed of parenchyma. The origin of successive rings of accessory cambium, their divisions and formation of vascular strands and parenchyma, and proliferation of parenchyma are very rapid. Thus the Beta root grows in thickness rapidly. All the parenchyma cells store nutrients that mainly contain sucrose.