Nitella: Vegetative Body and Reproduction | Algae | Botany

In this article we will discuss about the vegetative body and reproduction of nitella.

Vegetative Body of Nitella:

The plant body typically shows equisetoid habit with nodes and internodes and the usual whorled arrangement of lateral branches of limited growth, the so-called ‘leaves’. It is anchored to the sub­stratum by means of multicellular rhizoids.

The rhizoids do not show differentiation into nodes and internodes, but possess oblique septa. In addition to the function of anchoring, they also absorb mineral salts from the substratum. Each internode consists of a single elongated cell, often attaining a length of about 25 cm., and is never corticated like Chara.

Usually, the branches of limited growth are produced singly from the oldest lateral branch, but in some cases a second branch may develop from the next oldest lateral one. The growth of the primary or secondary axis takes place by means of successive divisions of the dome-shaped apical cell. In some cases, the basal nodes of the short lateral branches produce unicellular spinous outgrowths, the so-called stipules, which may also be sometimes branched.

As in Chara, the cells contain numerous discoid and oval chlo­roplasts without any pyrenoid and a single nucleus, and these are embedded in the peripheral layer of cytoplasm surrounding a large central vacuole. The nucleus multiplies by the process of amitosis. Protoplasmic streaming is also noticeable. The cell wall mainly consists of cellulose. The superficial layer is of an unknown com­position and is more or less gelatinous in texture in which deposi­tion of calcium carbonate takes place.

Reproduction in Nitella:

Nitella reproduces by vegetative and sexual methods.

Vegetative reproduction occurs at all stages in the life cycle of Nitella. It takes place by the formation of secondary protonemata originating from the basal node of the primary rhizoid or the rhizoidal node of protonema. Secondary protonemata sometimes develop from the dormant apical portion of the surviving nodes of an older plant after a period of perennation.

A fragment of the plant with a node, when placed under favourable conditions, may give rise to secondary protonemata. Occasionally, tuber-like out growths develop from the rhizoids or portion of the axis embedded in the substratum.

The plant is either   homo­thallic or heterothallic. Sexual reproduction takes place by oogamy. The essential features of reproduction are like those of Chara but with a few minor differences. As a general rule, the sex organs, nucule and globule, develop in close juxtapo­sition in homothallic species, but in several heterothallic ones they occur on different individuals.

They are usually borne on secondary-branches of limited growth and develop from the upper nodes of the primary laterals. They are ge­nerally so orientated that the nucule is directed downwards and the globule, upwards. Elongated one-celled branchlets the so-called brancteoles, usually develop from basal node of the globule and constitute a loose envelope around the nucule.

At maturity, the glo­bule is spherical, bright yellow or red in colour, while the oval nucule with its spirally coiled, bright green threads appear very conspicuous to the naked eye. The mode of development of the sex organs, the process of fertilization and embryogeny are more or less similar to those of Chara, It is to be noted, however, that the corona is made up of two tiers of cells.