100 PRACTICAL BOTANY. 



3. Mount a very little of the Spirogyra in water. Ex- 

 amine with the low power and notice that each filament is 

 made up of cells which are just alike. The plant is uni- 

 cellular, although at first sight it seems to have many 

 cells. The long filaments are to be accounted for by the 

 fact that one mode of reproduction, the asexual, is by 

 the transverse division of the cells, the new cells being 

 held together, end to end, by a very delicate, gelatinous 

 membrane. Any of the cells may divide. 



4. Examine with the high power. Notice the spiral 

 bands of chlorophyl the chromatophores or chlorophyl 

 bodies. The number of these bands differs in different 

 species. Several species may be present in the mount. 

 If not, mount specimens obtained from different localities 

 until a number of different forms of the chromatophores 

 have been observed. Draw three cells of each species 

 found. 



5. Notice the roundish bright spots that occur at inter- 

 vals in the chromatophores. These are the pyrenoids. 



6. Run iodine solution under the cover glass. Focus 

 upon filaments that are just beginning to take the stain. 

 If the Spirogyra has been in the sunlight for some time, 

 a ring of dark blue, almost black, particles will be seen 

 around each pyrenoid. These are starch granules. Keep 

 some Spirogyra in the dark for several hours. Test for 

 starch. Do you find it ? 



The chromatophores of chlorophyl-bearing plants are 

 the laboratories in which the starch is manufactured. 

 Keep some Spirogyra for one or two hours in water that 

 has been boiled to expel the carbon dioxide. Test for 

 starch. Do you find it ? If so, is it as abundant as in 

 Spirogyra kept in water from which the carbon dioxide 

 has not been removed ? What conclusion do you draw 

 as to the necessity of carbon dioxide in the formation of 

 starch? Keep Spirogyra in ordinary water in the sun- 



