76 TYPE STUDIES 



2. The one or more green spiral bands extending around in 

 the interior of the cell just under the cell wall. Focus on 

 the band above and below, following it around the cell. 

 D. Place a drop of salt solution (5 or 10 per cent) at the side of 

 the cover glass, and draw it under by means of a small piece 

 of filter paper applied against the opposite edge. Note the 

 contraction of a delicate membrane away from the cell wall, 

 so that the former immediately becomes apparent as a con- 

 tinuous membrane inclosing the green band and other contents 

 of the cell. This membrane and its contents comprise the 

 living substance, or protoplasm, of the Spirogyra cell, and is 

 the living cell or protoplast; its structure will be taken up in 

 the next section. The cell wall is composed of cellulose which 

 is not protoplasmic in character, being formed by the proto- 

 plast and constituting a protective case around it. 

 57. The structure of the protoplast of Spirogyra.* * 

 A. Mount a slide of living Spirogyra as described in Sec. 56, B, 

 to study the protoplast. Note imder h.p. : 



1. That each green spiral band, called a chromatophore, con- 

 'tains several denser structures termed pyrenoids. 



2. A globular or elliptical structure, the nucleus, near the 

 center of the cell, held in position by delicate protoplasmic 

 strands which radiate outward to the cell walls. The out- 

 line of the nucleus will probably be clearer when the 

 material is stained with iodine, as described in B. 



3. A delicate lining, or plasma membrane, next the cell wall 

 under which the chromatophore lies imbedded in a layer 

 of protoplasm. The plasma membrane was demonstrated 

 when the protoplast was drawn away from the cell wall 

 by the salt solution, as described in Sec. 56, D. 



4. That the interior of the protoplast contains no solid or 

 semifluid substance, except possibly some minute granules, 

 and must consequently be either liquid or gas. Which 

 alternative is suggested by the experiment with the salt 

 solution (Sec. 56, D) ? 



