42 COMMON POND-SCUM. 



c. Search for various stages in the growth of the conju- 

 gating tubes, and observe whether tubes from con- 

 jugating cells always begin in pairs; also whether one 

 cell ever conjugates with more than one other cell. 



5. The cell contents. 



a. By studying various specimens, trace the changes from 

 the vegetative condition through the several stages of 

 disintegration of the chlorophyll band and contraction 

 of the protoplasm to the formation of a rounded green- 

 ish-brown mass; noticing at the same time that this 

 change is contemporaneous with the formation of the 

 conjugating tube. Usually all stages are easily found. 



b. Where the conjugating tube is fully formed, note that 

 one cell is empty, and the connected cell contains a 

 single mass, the spore produced by the conjugation. 



c. When the cells of two filaments have conjugated see 

 whether all the zygospores formed lie in the cells of one 

 filament of the pair. 



6. The mature zygospore. Note: 



a. Shape and color. 



b. Contents. 



c. The wall of greater or less thickness, usually resolvable 

 into two or more layers of different colors. 



7. Make drawings to illustrate the parts and changes of the 

 reproductive filaments. 



ANNOTATIONS. 



In form and manner of growth Spirogyra shows no 

 essential features not seen in plants already studied, 

 except the arrangement of the protoplasm and chlorophyll 

 bodies. The filaments are built on the plan of Oscillatoria 

 and Ulothrix, with the cells larger, and the sheath so 

 much reduced that it can be demonstrated only with 



