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 

 sensitive to light and, therefore, of 

 some use in directing the movements 

 of the individual. In certain species 

 a bright red pigment is often so 

 abundant that, when the plants are 

 numerous, they cause pools to ap- 

 pear red and, when blown over the 

 snow, produce the " red snow " of 

 arctic and alpine regions. 



In the number of cells constituting 

 the plant body, Chlamj^domonas 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 zoospores and gametes. 

 In forming zoospores 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 zoospores escape from 

 the mother cell and enlarge to the parent size. Under certain 

 conditions the protoplast may form many small zoospore-like 

 cells which escape from the mother plant and fuse in pairs to 

 form resting zygospores which later form new plants. Since 

 these small zoospore-like cells fuse, they are gametes or sex cells 



Fig. 259. — Chlamydomonas, 

 a simple motile Green Algae. 

 At the left an individual, show- 

 ing the cilia, the large cup- 

 shaped chloroplast (c) con- 

 taining a pyrenoid, the nucleus 

 (n), the two pulsating vacuoles 

 (p), and the red pigment spot 

 represented by a black dot near 

 the pulsating vacuoles. At 

 the right an individual which 

 has formed two zoospores. 

 X 300. 



