186 PEACTICAL BOTANY 



that is set free is a new plant and may continue to grow until 

 it assumes the proportions of the old one. This is essentially 

 the same kind of reproduction that is seen in Nostoc, except 

 that here, instead of having a heterocyst, the dead cell does 

 not become enlarged. Oscillatoria plants may also break at any 

 point to produce new individuals. 



171. General characteristics of the blue-green algae. In 

 addition to the types of blue-green algae that have been dis- 

 cussed, many other kinds are abundant. They are found in 

 the same kinds of regions as those that have been presented 

 in the preceding paragraphs. Members of this group have the 

 characteristic Hue-green color, with this color pretty evenly dis- 

 tributed throughout the interior of the cells. The blue-green 

 algae are extremely simple in structure, being one-celled plants 

 (as Grloeocapsa), or plants made up of cells arranged in rows 

 so as to form simple chains (as Nostoc), or filaments (as Oscil- 

 latoria). Some of the members of the group are more complex 

 than Oscillatoria, as Grlwotrichia and Rivularia, which are com- 

 monly found as small, glistening, jelly-like balls attached to 

 sticks and to the stems of other plants. They are usually 

 found in shallow fresh-water lakes, or sometimes free-floating. 

 The entire group consists of plants that are relatively simple 

 in form and structure. The cells are simple, and definitely 

 organized chloroplasts. are not present. Nuclei of the kind 

 known in the other algae and in the higher plants have not 

 been demonstrated in this group, although fragments that 

 resemble the nuclei of higher plants have been found. 



Most of the members of the group have a jelly-like cover- 

 ing, and in many forms this holds the plants together in colo- 

 nies. This covering seems to be of advantage to the plants 

 during periods of drought by regulating the rate of drying. 



The water or moist habitat and the simplicity of structure 

 suggest the simple way of securing food material, namely by 

 absorbing it directly through any part of the wall of the plant. 

 By means of chlorophyll, members of this group may manu- 

 facture foods through the process known as photosynthesis. 



