102 PRACTICAL BOTANY. 



the exception of the end cell, which differs from the others 



only in having its extremity more rounded. 



.'9. Run* Schiiltee's solution under the cover glass of a 

 g fresh .mount. .NoUce and describe the effect on the cell 

 ; wall and ion -the "Cell' contents. 



10. Find the nucleus in a fresh mount. In some spe- 

 cies the nucleus is very prominent ; in others it can be 

 made out only after special treatment. In difficult cases 

 leave some Spirogyra in a one per cent solution of picric 

 acid for several hours, wash out the acid in water, followed 

 with 35 per cent alcohol, stain in Grenadier's borax car- 

 mine, wash again in 35 per cent alcohol, and mount in 66 

 per cent glycerine. 



By searching material from different localities, good 

 specimens are usually found which show the nucleus with- 

 out this special treatment. Draw a cell, showing all the 

 details of structure, especially the nucleus, nucleolus, and 

 the manner in which they are suspended in the center of 

 the cell by strings of protoplasm running to the pyrenoids. 

 (Compare Fig. 57, A and B.) Treat different mounts of 

 material showing the nucleus with iodine, alcohol, ten per 

 cent salt solution, and with different stains. 



11. Find material in the conjugating condition. Here 

 again it may be necessary to search the material from 

 several localities. Find, if possible, specimens in which 

 the zygospores are formed in the cells of one of the fila- 

 ments, and others in which they are formed in the conju- 

 gating tubes between the filaments. Draw in detail 

 typical cases. 



12. Try to find material in which the contents of the 

 cells of a filament have become aggregated into spores 

 without conjugating with the cells of another filament. 

 Such cases may be recognized by the fact that the cell 

 walls are still entire and show -no indications of having 

 given out conjugating tubes, or of having received such 



