114 MORPHOLOGY AND LIFE HISTORY 



5. Does the cell- wall of the receiving cell serve as the 

 cell-wall of the zygospore, or does the latter form a 

 new wall? 



6. In a sentence define the term supplying cell, using 

 the words gamete and conjugation. 



7. If fresh material is studied, describe any observed 

 differences in color between the mature zygospore 

 and the non-conjugating cells; any structural dif- 

 ferences between the cells of a supplying filament 

 and those of a receiving filament. Do you observe 

 any evidence of sexual differentiation in the 

 filaments? 



8. Can you detect any constant structural difference 

 between supplying and receiving cells in size, or in 

 the size of the cell organs (e.g., width of chlorophyll 

 bands, diameter of pyrenoids, etc.) ? 



9. Explain whether Spirogyra represents a condition 

 of isogamy or of beterogamy. 



10. Make drawings of all the following features shown 

 by your material, with each cell about 50 mm. long. 



(a) Two adjacent cells in which the conjugation- 

 tubes are just beginning to develop. 



(b) Two adjacent cells in which the conjugation- 

 tubes have just met. 



(c) Two adjacent cells in which the active (supply- 

 ing) gamete is passing through the conjugation- 

 tube. 



(d) Two adjacent cells in which the passage is 

 complete. 



(e) Two adjacent cells after conjugation is com- 

 plete. Show carefully and accurately the details 

 of structure of the zygospore. 



11. Study stages in the germination of the zygospore 

 as shown on the chart. State, in order, the proc- 



