CHAPTER XXIV 

 THE ALG^i 



271. Definition ; Occurrence. — The algce comprise all of 

 the plants below the liverworts and mosses with the capacity 

 for photosynthesis. They constitute a series of the division 

 Thallophyta (see Sect. 261). 



Most algae are aquatic, some inhabiting fresh and others 

 salt water, but a few groups flourish in merely damp situa- 

 tions, such as on moist earth, bark, or wood. Still others 

 (constituting the photosynthetic part of lichens) grow in 

 partnership with certain fungi (Sect. 327). 



272. Classes of Algae. — Algse are divided, mainly on 

 the basis of their modes of reproduction, into six great 

 groups, as follows: 



Class 1. Blue-green algse, CyanopliycecE. 



" 2. Diatoms, Diatomacece. 



" 3. Conjugating algee, Conjugate. 



" 4. Green algae, Chloropliycece. 



" 5. Brown algae, PTiceophycece. 



" 6. Ked algae, Rhodophycece. 



The color, though not a basis of classification, forms a 

 very convenient means of naming and roughly distinguish- 

 ing some of the groups ; it does not, however, serve to 

 distinguish Class 3 from Class 4. 



1 See Bergen and Davis' Principles of Botany and Whipple's Microscopy 

 of Drinking Water, Wiley & Sons, New York. 



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