Tag: root

The root hairs of  plants are actually tubular outgrowth of trichoblast, a hair-forming cell present on the epidermis of roots. These help the plants to increase the surface area of their roots so as to absorb the mineral nutrients present in the soil. In most dicotyledons and monocots, the root hairs are unicellular, thin walled and un-branched  structures and are short lived. However, there are exceptions such as the ones found in the aerial adventitious roots of Kalanchoe where these are multicellular.

A typical root has four regions. 

Velamen is a spongy, multiple epidermis that covers the roots of some epiphytic or semi-epiphytic plants, such as orchid and Clivia species. The velamen of an orchid is the white or gray covering of aerial roots. It is many cell layers thick and capable of absorbing atmospheric moisture and nutrients. Often, the roots of orchids are associated with symbiotic fungi or bacteria. The latter may fix nutrients from the air. This functionality allows the orchid to exist in locations that provide a reproductive or vegetative advantage such as improved exposure or reduced competition from other plant species. The velamen also serves a mechanical function, protecting the vascular tissues in the root cortex, shielding the root from transpirational water loss and, in many cases, adhering the plant to the substrate. Velamen is not found in breathing roots of halophytes, parasitic plants and all aerial roots. The typical orchid root has a stele of comparatively small diameter. It is surrounded by a cortex which is further enveloped by a highly specialized exodermis, most of which at maturity do not contain protoplasm. A few cells, however, are living and allow the passage of water through them. The exodermis is surrounded by velamen, consisting of one to several layers of cells, which can develop root hair under proper environmental conditions. 

Inulin, is a levulosan which is found  among numerous angiosperm families. This carbodyhrate is found in the cell sap of some species, while in others it accumulates as an amorphous material. However, in some species this is form as inulin crystals and are found deposited in living tissues. This is found in colloidal condition in the roots of dahlia, artichoke and other members of Compositeae family. In Dahlia roots, the inulin depositions appear like fan like crystals.

Many plants growing in aquatic habitats do not possess roots because there is little requirement for absorption of water and mineral salts, e.g., Wolffia, Utricularia, Myriophyllum, Ceratophyllum. In other aquatic plants, roots develop only for balancing (e.g., Lemna, Pistia) and fixation (e.g., Hydrilla). The root cap is a section of tissue at the tip of a plant root. It is also called as calyptra. Root caps contain statocytes which are involved in gravity perception in plants. If the cap is carefully removed the root will grow randomly. The root cap protects the growing tip in plants. It secretes mucilage to ease the movement of the root through soil and may also be involved in communication with the soil microbiota. Since, roots in Pistia are only for balancing, root cap is not required. So, root cap is absent in Pistia. 

The thick waxy layer covers  the surface of aerial organs is called Cuticle. It is made up of waxy substance called cutin. It is thin in mesophytes and highly thick in xerophytes. It is absent in hydrophytes and underground organs.

A. Dermatogen is the primary meristem that forms the outermost layer of a plant or a plant part and forms the epidermis.

B. Calyptrogen is a specialized layer of rapidly dividing cells present at the root tips which continuously divide to form the root cap is formed.

C. Wound cambium is formed within amasses of cells (callus) which grow over the injured surface of a wound to heal and repair that part.

D. Vascular cambium is a lateral meristem that develops within the vascular bundles to produce xylem to the inner side and phloem to the outer side and is also called fascicular cambium.

So, the correct answer is A.