CHAPTER XXIV 
THE ALG! 
271. Definition ; Occurrence. — The alge 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 alge 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 Alge.— Algz are divided, mainly on 
the basis of their modes of reproduction, into six great 
groups, as follows: ; 
Crass 1. Blue-green alge, Cyanophycee. 
2. Diatoms, Diatomacee. 
3. Conjugating alge, Conjugate. 
« 4. Green alge, Chlorophycee. 
5. Brown algz, Pheophycee. 
6. Red alge, 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. 
1See Bergen and Davis’ Principles of Botany and Whipple’s Microscopy 
of Drinking Water, Wiley & Sons, New York. 
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