BIOLOGICAL INTRODUCTION. 



green threads. Each thread is made up of a number of cylindrical 

 cells placed end to end. In each cell there are one or more spiral 

 bands of a bright green color. These contain the chlorophyll of 

 the plant and are called chromatophores. At intervals in the band, 

 small, round bodies may be seen which contain proteid substance. 

 Aside from the spiral bands and the thin layer of protoplasm lin- 

 ing the cellulose cell wall, the cell space is filled with so-called cell 

 sap. This consists of water in which certain inorganic and organic 

 substances are dissolved. The nucleus may be either central or 

 peripheral. The growth of the plant is accomplished by cell 

 division in the long axis, maintaining the thread formation. 



Reproduction takes place through conjugation. This is a good 

 example of sexual reproduction. Ordinarily this occurs in the fol- 

 lowing manner. Cells from two adjoining filaments send out pro- 

 trusions toward each other. These meet and join, their adjoining 

 membranes becoming absorbed so as to form one continuous tube. 

 The cell contents of both contract, the one before the other, and 

 the contents of one cell run through the tube into the other, nucleus 

 uniting with nucleus, chromatophore with chromatophore. This 

 is typical of sexual reproduction in both plants and animals. In 

 this case, the new cell thus formed is called a zygospore. This, 

 which is at first spherical in shape, without any distinct cell wall, 

 increases in size by the imbibition of water, assumes the form of an 

 ellipse and develops a hard envelope which is impermeable to 

 water. In this condition the cell can withstand drying and con- 

 siderable variations in temperature. When the plant again ger- 

 minates, the cell wall is burst and the contents grow out into a new 

 filament. 



Practicum. Observe, with unaided eye, a mass of spirogyra. 

 Mount a few filaments and observe under first low and then high 

 power of the microscope. Describe the structure. Make a draw- 

 ing. Stain a specimen with carmine, after fixation in picric acid. 



To observe the phenomena of reproduction, examine a tresh 

 specimen that has been kept in the cold, over night. 



Observe, from time to time, a specimen that has been kept in 



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