78 TYPE STUDIES 



D. Place some living Spirogyra in alcohol and after several hours 

 note the extraction of a green pigment, chlorophyll, from the 

 chromatophores in the filaments. What change in the color of 

 the filaments ? The alcohol may be evaporated by gentle heat 

 in a shallow dish, leaving the chlorophyll as a green residue. 



58. Photosyntliesis in Spirogyra. 



A. Perform the experiment in photosynthesis outlined in Exp. XXXI, 

 using Spirogyra for the subject. 



B. Place Spirogyra for a day or two in the dark and then test for starch 

 as described in Sec. 57, B, 2. Return the material to sunlight, and after 

 several hours test again. Compare results. 



59. Cell reproduction in Spirogyra. Nevf cells arise in Spirogyra 

 either (1) by cell division or (2) by cell unions to form reproduc- 

 tive cells called zygospores or zygotes. 



60. Cell division in Spirogyra. Search a slide of Spirogyra for 

 adjacent cells in the same filament considerably shorter than the 

 average size. Such a pair will probably be sister or daughter cells 

 formed by the division of a mother cell. The division of the 

 mother cell is preceded by the division of the nucleus, after 

 which a partition wall of cellulose is formed between the daughter 

 nuclei. Spirogyra is, however, not a favorable subject for the 

 study of nuclear and cell division (Sec. 65). 



61. Cell unions to form zygospores in Spirogyra.* * At times 

 Spirogyra fruits.'^ 



A. If living material is available, note the frequent change 

 in color and occasional dirty appearance of the filaments. 

 Mount fruiting material (either living or preserved) teased 

 out well. Note : 



1. That certain cells contain thick-walled oval or elliptical 

 structures densely filled with protoplasm and food material. 

 These are zygospores or zygotes. 



2. That the zygospores are formed by the union or conjuga- 

 tion of cells. In some species of Spirogyra the cell unions 

 are between different filaments, in other species between 



1 The ievms fruit a,nA fructification will be used in Part II in an untechnical 

 sense to designate various forms of reproductive organs and processes. 



