Hydrodictyon: Vegetative Body and Reproduction | Algae | Botany

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

Vegetative Body of Hydrodictyon:

All species of Hydrodictyon form colonies of a definite num­ber of cylindrical or ovoid cells (coenobia) which are united to form a free-floating, hollow, cylindrical network, usually closed at either ends and reaching a length as much as 15-30 cm. The meshes of the reticulum are formed by the union of elongated.

Each mature cell is multi-nucleate and the nuclei lie in the peri­pheral layer or cytoplasm internal to the cell wall and surround­ing a large central vacuole. The chloroplast is peripheral, reticu­late and possesses numerous pyrenoids.

Reproduction in Hydrodictyon:

Hydrodictyon reproduces both asexually and sexually. Any cell of the coenobium may form zoospores, but the ad­jacent cells may or may not show any sign of zoospore-formation. Thousands of uninucleate, biflagellate zoospores are produced from the protoplast of the mature coenocytic cells by progressive clea­vages.

They do not escape from the mother cell, but remain con­fined within the wall of the parent coenocyte and exhibit a some­what restricted movement. The necessary space for the movement of the zoospores is provided by the extension of the longitudinal cell walls and by the diminution in size of the vacuole.

They finally come to rest, arrange themselves in straight rows in three direc­tions and touching one another withdraw their flagella, secrete membranes and form a new coenobium by the elongation of these cells. The young coenobium at first remains enclosed within the mother cell wall, which later on gelatinizes and liberates the new coenobium.

Hydrodictyon is a monoecious and the isogametes formed from the same coenobium may conjugate in pairs. The gametes are pro­duced in the same way as the zoospores but they are much smaller in size. Further,they are liberated from a parent cell through a hole in the cell wall. After fusion of two gametes, their flagella are withdrawn immediately and a spherical zygote with a thin cell wall results.

This zygote gradually increases in size, appears red in co­lour due to formation of haematochrome and accumulates oil as reserve food. After a period of rest, this zygote nucleus undergoes reduction division and the protoplast is divided into four large, biflagellate zoospores.

Each zoospore contains numerous discoid chlo­roplasts without pyrenoids. They are finally liberated by the rup­ture of the wall of the zygote and swim for some time. After the period of swimming, a zoospore comes to rest and develops to form a polyhedral cell resembling some species of Tetraedron.

This may be regarded as an aplanospore. This polyhedral cell greatly in­creases in size forming zoospores in the usual way, and these again unite to form a new coenobium, which is liberated by the rupture of the cell wall.