SPIROGYRA 
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cell. As long as the cell is full of chlorophyll, the cytoplasm 
cannot be seen (Figure 283). 
Pleurococcus makes its own food as larger plants do, and 
it is able to digest the starch and protein which it makes. 
Whenever a number of pleurococcus cells are examined, 
some are found to be dividing. In this division the nucleus 
forms two nuclei which move apart. A partition wall forms 
and two cells take the place of the old or parent cell. This 
method, called fission (Latin, fissus, cleft), is the simplest 
form of reproduction. It is a form of asexual or vegetative 
reproduction, as it takes place without the union of egg and 
sperm. In pleurococcus the cells do not always separate at 
once, but form groups of two, three, or more cells (Figure 
283). 
SUMMARY 
This simple unicellular (one-celled) green plant, pleu¬ 
rococcus, lives and makes its own food and produces new 
cells. While there are no flowers and seeds as in the plants 
already studied, yet this plant is able to reproduce itself. 
All the important life processes found in plants take place in 
the simple, single cell. 
LABORATORY STUDY OF PLEUROCOCCUS 
Study this as an example of a plant which consists of a single cell, 
but still performs all the processes common to complex plants. Soak a 
bit of bark and scrape it gently to get the pleurococci cells, some of which 
may be in groups. Place on a slide and examine with high-power 
microscope. Draw a single cell and a group of cells. Label cell wall 
and nucleus. 
262. Spirogyra. — This plant is best known as the “ pond 
scum v which grows in most fresh-water ponds and in slow- 
running streams. It may be kept for some time in glass 
dishes in a laboratory. Instead of being made up of round 
cells or clusters of cells, the cells of spirogyra are cylindrical 
in shape and are attached end to end. This results in long, 
