Spirogyra, an Introduction
Spirogyra is a member of the Algae. These are simple plants ranging from single-celled organisms (Chlamydomonas, Euglena) to complex seaweeds. They contain chlorophyll and make their food by photosynthesis. Spirogya is a filamentous alga. Its cells form long, thin strands that, in vast numbers, contribute to the familiar green, slimy ‘blanket weed’ in ponds. Seen under the microscope, each filament consists of an extensive chain of identical cells. Each cell contains a helical chloroplast, a nucleus, cytoplasm and a vacuole enclosed in a cellulose cell wall.
Growth
Each cell can divide transversely and grow to full size thus increasing the length of the filament. When the filament breaks, this is a form of asexual reproduction but there is a sexual process called conjugation.
Conjugation
At certain times of the year, tubular structures grow out from each cell of a pair of filaments lying parallel to each other. The tubes join up to make a passage between each cell and its partner. The chloroplasts and other structures become less distinct and the cytoplasm pulls free from the cell wall to form a rounded structure. The cytoplasmic contents of the cells now act as gametes. The gametes of one filament then pass through the tubes (conjugation tubes) and fuse with the gametes of the cells of the adjacent filament and the nuclei fuse to form a zygote.
A resistant wall develops around the zygote to form a spore and, when the cell walls of the filament break down, the spore is released and sinks to the bottom of the pond. The spore can survive adverse conditions such as low temperature and shortage of light.
When conditions become favourable again, the spore wall breaks open and a new spirogyra filament grows out.
For illustrations to accompany these notes see Protista
See also: Video of Spirogyra
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