CHLAMYDOMONAS 303 
Chlamydomonas. —In Chlamydomonas (Fig. 259), which is 
regarded as one of the simplest of the Volvocales, the habit of 
colony formation is lacking and, therefore, each individual swims 
about independently. This plant is common in fresh water and 
when seen swimming about under the microscope might be mis- 
taken for a protozoan, a one-celled animal which it resembles. 
The Plant body consists of a more or less globular protoplast 
closely invested by a thin membrane through which the two long 
cilia project at the forward end. 
There is a large cup-shaped chloro- 
plast, in which there is a protein 
body called pyrenoid. The nucleus 
is in the cup of the chloroplast; at 
the base of the cilia are two con- 
tractile vacuoles; and not far from 
these is the red pigment spot or 
eye spot which is supposed to be Fig. 259.—Chlamydomonas, 
sensitive to light and, therefore, of a simple motile Green Algae. 
some use in directing the movements At the left an individual, show- 
of the individual. In certain species 8 the cilia, the large cup- 
P é shaped chloroplast (c) con- 
a bright red pigment is often so itonnbia Bamenord, the aaeli 
abundant that, when the plants are (n), the two pulsating vacuoles 
numerous, they cause pools to ap-  (p), and the red pigment spot 
pear red and, when blown over the _ vepresented by a black dot near 
snow, produce the “zed snow” of ie puting, vm 
arctic and alpine regions. haa fonued: tae -anspares, 
In the number of cells constituting x 300. 
the plant body, Chlamydomonas is 
as simple as any of the Blue-green Algae, but in having a chloro- 
plast and well-defined nucleus and cytoplasm, it shows considerable 
advancement. 
Reproduction takes place by means of zoéspores and gametes. 
In forming zoéspores the plant becomes quiescent and the proto- 
plast divides into two or more ciliated cells which are miniatures 
of the parent. These daughter cells or zodspores escape from 
the mother cell and enlarge to the parent size. Under certain 
conditions the protoplast may form many small zodéspore-like 
cells which escape from the mother plant and fuse in pairs to 
form resting zygospores which later form new plants. Since 
these small zodspore-like cells fuse, they are gametes or sex cells 
