264 COLLEGE BOTANY 



(antheridium and oogonium) containing highly developed ga- 

 metes (sperm-s and obspores}. The OhLorophyceeo can be di- 

 vided into the following orders: 



1. Volvocales unicellular, single or colonial, usually motile 

 species (page 264). 



2. Protococcales unicellular, colonial, non-motile species 

 (page 266). 



3. Confervales multicellular, simple or branched filaments 

 or flat branched filaments or flat thallus structures; reproduction 

 by non-sexual cells or by gametes (page 267). 



4. Siphonales usually unicellular but often multiiiuclear, 

 filamentous species, sometimes branched ; reproduction by well- 

 defined organs (page 268), 



5. Conjugates unicellular species or multicellular species ; 

 reproduction by conjugation (page 269). 



6. Charales a group whose place in the plant kingdom is 

 questioned (page 271). 



The order Volvocales is composed of unicellular and colonial 

 forms, which are usually ciliate and motile and therefore have 

 these characters in common with one of the groups of lower uni- 

 cellular animals known as Flagellates. Among the most com- 

 mon genera are Chlamydomonas, Sphcerella, Pandorina, Eudo- 

 riiia and Volvox. 



Chlamydomonas (Fig. 119, a d} and Sphcerella are unicellu- 

 lar forms which have the power of locomotion by means of cilia. 

 This power of locomotion is so highly developed that these 

 species might very readily be mistaken for animals, if it were 

 not for the fact that they contain chlorophyll and perform the 

 same physiological functions as other chlorophyll-bearing 

 plants. Each individual has a red spot known as the " eye spot," 

 which is supposed to be sensitive to light. This red pigment is 

 sometimes so abundant as to give pools of water a reddish tinge. 

 The so-called " red snow " of the arctic regions is in reality due 

 to masses of algae belonging to this group in which this red 

 pigment is very highly developed. The individual cells eventu- 



