CHAPTER VI 
ALG 
57. General characters.—Alge are the simplest green 
plants, and it is thought that the higher plants have been 
derived from them. They grow in the water, and hence 
their habits are adapted to a water environment. They are 
often called seaweeds, but although they are very abundant 
along seacoasts they are also abundant in fresh waters. 
Some of them are so small that the individual bodies are 
visible only under the microscope, and there is every grada- 
tion in size from this to the bulky bodies of certain marine 
forms. 
Although all Algze contain chlorophyll, and hence are 
able to make their own food (§ 14), they do not all appear 
green; for in many of them the chlorophyll is obscured by 
other coloring matters. The four great groups of Alge are 
named from the general color of their bodies, although 
it must be remembered that they all contain chlorophyll, 
which makes them independent. Some representatives of 
each group are selected for description, but they or others 
like them must be examined before any real knowledge of 
them can be obtained. 
1. BLUE-GREEN ALG® (Cyanophycee) 
58. Gloeeocapsa.—These plants form blue-green or olive- 
green patches on damp tree trunks, rocks, walls, etc. By 
means of the microscope these patches are seen to be com- 
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