CHAPTER XII 

 THE BLUE-GREEN ALG^E (CYANOPHYCEJE) 



163. Introductory. The life habits, size, and structure of the 

 blue-green algae are such that we can obtain the best notion 

 of the whole group by selecting for discussion a few represent- 

 ative plants. " Representative plants " cannot fully represent 

 this or any other group, any more than three or four selected 

 students would adequately represent an entire school. How- 

 ever, in an elementary textbook it is not advisable to present 

 a large number of plants from each group. 



164. Where found. The blue-green algae are found in pools 

 of stagnant water, along shores of streams, lakes, and oceans, 

 in places where the water contains considerable organic matter. 

 They may appear as coatings to sticks, stones, etc., as float- 

 ing pieces of dirty, bluish-green material, or as small masses 

 free-floating or attached and held together in jelly-like balls. 

 Usually they may be readily distinguished from other algae 

 by the distinct bluish-green color. 



165. Gloeocapsa: structure and nutrition. In stagnant water 

 such as is found in old pools, horse tracks in open fields, and 

 sometimes in aquarium jars in the laboratory, the plant known 

 as Gloeocapsa may appear as bluish-green fragments floating 

 or adhering to the sides or bottom of whatever may contain 

 the water in which it is growing. These fragments are made 

 up of a great many plants, each one so small that when alone 

 it cannot be seen without magnification. The appearance of 

 the masses of many plants may be thus determined, but that 

 of a single plant can be determined only by the aid of a com- 

 pound microscope. 1 A single plant when separated from the 



1 In the first studies of the single-celled algae it is often better to use a 

 good specimen under a compound microscope as a demonstration than to 



180 



