272 THE AMERICAN MONTHLY [Aug. 



green color is due to chlorophyll; it is the same substance 

 as that found in the leaves of higher plants, and has im- 

 portant relations to the chemical changes in plants. 

 Can you recognize a nucleus in the large cells? Test to see 

 if it stains deeply with iodine. Can you prove the 

 presence of a definite and strong cell- wall? It is com- 

 posed of cellulose (to prove this, stain with iodine and 

 then with strong sulphuric acid; it becomes blue). Study 

 different colonies, noting exactly the size and position of 

 the component cells, and attempting to decide the way in 

 which they have been formed. Do division lines fall in 

 several different planes? What sort of a form would 

 result from the continued division of the cells if they did 

 not become separated? Treat some Protococcus with 

 strong alcohol, noting the green color which is imparted 

 to the latter, then examine to note that the chlorophyll 

 has been dissolved now stain and show that protoplasm 

 is left, filling the cell. If possible study the motile stage 

 of Protococcus and recognize the flagella (see Parker for 

 details.) 



18. Spirogyra. — Mount pieces of the filaments of 

 spirogyra in water and study single filaments. Decide 

 whether they branch ; locate the cells; are all of the same 

 shape and size? Do you find any indication of the for- 

 mation of cells by fission? Examine a single cell; locate 

 its side and end walls, and determine their thickness ; 

 locate the chlorophyll band; is it a spiral? Is it in the centre 

 or on the wall of the cell? Follow its winding by focus- 

 ing. How many spiral bands do you find ? Is the num- 

 ber the same in all the cells of the same filament ? Does 

 it vary in different filaments. Do they pass from one 

 cell to the next? Note the crenated margin oi t\\Q band, 

 and the numerous denser green globules, pyrenoids. 

 Locate the pyrenoids carefully in an exact drawing of one 

 cell. Search through the cell for protoplasm, locate the 



