62 PRACTICAL BOTANY. 



OSCILLATORIE^E. PRACTICAL STUDIES. 



1. Collect a considerable quantity of the dark blue- 

 green plants from any of the above-mentioned locations, 

 dry and pulverize it, and place it in a clear glass dish 

 with some water for several hours. The water dissolves 

 the coloring matter known as phycocyanin and becomes 

 bluish. Remove the water, add strong alcohol, and boil. 

 The alcohol becomes yellowish green by dissolving out 

 the chlorophyl. 



2. Mount a little of the fresh Blue-Green Slime in 

 water, i.e., place it on a microscope slide in a small drop 

 of water and cover with a cover glass. Under both low 

 and high powers of the microscope study the oscillations 

 of the filaments. Notice the tendency of the filaments 

 to radiate from a center. 



3. Study the cells of a filament. Note the finely 

 granular protoplasm and its uniform distribution in the 

 cell. Compare a branch of Nostoc, .noting the sizes of 

 the cells and the positions of the heterocysts or enlarged 

 cells in the Nostoc. Find short filaments of Nostoc that 

 have broken off at the heterocysts to form hormogonia. 

 Such filaments are frequently found in stagnant water. 

 Draw part of a filament of Oscillaria and one of Nostoc, 

 showing the characteristic structures. 



4. Observe the gelatinous sheath inclosing the fila- 

 ment. This is much more distinct in some species than 

 in others. In some species it is wholly wanting. In diffi- 

 cult cases it is best seen at the broken ends of filaments. 



5. Notice the turgidity of the cells, i.e., their swollen 

 appearance, due to the fact that the internal pressure of 

 the water that has been absorbed by the protoplasm is 

 greater than the external pressure. This is best observed 

 at the broken ends of filaments where the cell wall is 

 bulged out by the internal pressure. 



