216 



ESSENTIALS OF BOTANY 



OSCILLATORIA, — ONE OF THE BLUE-GREEN ALG^ 



273. Occurrence. — Oscillatoria may occur floating in 

 stagnant water, about watering troughs or outlets of drains 

 and sewers, or on pots in greenhouses. In general it flour- 

 ishes in the presence of dissolved and decaying organic 

 matter. 



274. Gross Structure. — Examine -with the magnifying glass a bit 

 taken from a growing mass of the plant and left for some hours in 



a white saucer with a little water. Note : 

 (o) The color. 



(b) The filaments radiating from the 

 rather compact mass of the plants. 



275. Minute Structure. — With m.p. 

 note : 



(a) The shape of the filaments. Are 

 they branched ? 



(i) Their movements. Describe these. 

 Sketch several filaments. 



With h.p. note : 



(c) The shape of the tip of a filament. 



(d) The coin-shaped cells of which the 

 filaments are made up. 



(e) The occasional occurrence of a dead 

 cell, leaving a transparent place in the 

 filament. 



(/) The delicate sheath inclosing the filament (best seen where 

 a dead cell occurs). Make a careful drawing showing the points 

 (c, d, e,f) above mentioned. 



276. Discussion. — Oscillatoria is a plant of very low 

 organization, marked, for example, by the absence of a 

 well-defined nucleus in the unit cells of which the fila- 

 ments are composed. Each cell is an individual plant, 

 although, as the student has seen for himself, they live in 

 communities. The flattened form of the cells is evidently 



F:g. 150. Gloeocapsa, one 

 of the Lowest of the Bhie- 

 Green Algae, (x 300.) 



A-E, successive stages in the 

 development of new indi- 

 viduals from a parent-cell. 



