222 GENEKAL BOTANY 



CHLA M YDOMONA S 



In the genus Chlamydomonas, the species of which are common 

 in stagnant water, each plant (Fig. 116) is a single cell with a 

 thin cell wall through which two delicate protoplasmic filaments, 

 called flagella, can be seen to protrude. These flagella are minute 

 extensions of the outer layer of the protoplast of the Chlamydo- 

 monas cell, and it is by the contractile, whiplashlike movements 

 of these flagella that the organism is propelled through the water. 

 These movements are often seen to be toward a source of light, 

 indicating that the organism is sensitive to light of different inten- 

 sities. This sensitiveness is thought to be located in a brick-red 

 ( spot, erroneously called the eyespot, which 



contains a brick-red coloring matter by which 



Chlamydomonas 

 and its near rel- 

 atives are often 

 ^ ^^r ^ v W VOr recognizable. 



Ihe plant Gamete Conjugation Zygotes o i , 



formation Reproduction 



FIG. 116. Sexual reproduction of Chlamydomonas takes place, as 



in Protococcus, 



by cell division ; but the cell division in Chlamydomonas results 

 in a cleavage of the protoplast within the mother-cell wall into 

 two or more separate protoplasts, which then round up, form 

 flagella, and develop either asexual reproductive cells, called 

 zoospores, or sexual cells, called gametes. The gametes are fre- 

 quently produced in greater numbers than the zoospores, and 

 hence are smaller. The gametes are liberated in the water by the 

 rupture of the cell wall of the original Chlamydomonas cell, and 

 conjugate in pairs to form a zygote cell. This zygote cell then 

 enlarges, secretes a protective cell wall, and undergoes a period 

 of rest. It germinates under favorable conditions to form asexual 

 zoospores similar to the gametes in appearance, which enlarge 

 to form new free-swimming plants. In some species the gametes 

 are of unequal size, foreshadowing the differentiation in the size 

 of gametes which obtains in higher forms of algae. In asexual 

 reproduction the zoospores simply enlarge and form a new plant. 



