LABORATORY STUDIES 183 



(Cosmarium) of a bright green color may frequently be found. 

 The hirge kuiatc desmids (Closteriuni) are often more common. 

 In the hitter the clear protoplasm at each end is always stream- 

 ing rai)idly. 



(c) Round Diatoms may be obtained of dealers in laboratory 

 material, or mounted slides may be used. A few Round 

 Diatoms may be found occasionally in fresh-water ponds, and 

 they often occur on the surfaces of marine seaweeds. 



(d) Collect a little of the brownish-yellow scum which in 

 earl}^ si)ring gathers on the top of the water of brooks, ditches, 

 and pools. Mount in water and examine with a high power. 

 Hundreds of Flat Diatoms may be seen moving rapidl}- in 

 ever}^ direction across the field. In any such preparation many 

 species of various shapes will be found. The prevailing forms, 

 however, are much flattened and somewhat diamond shaped 

 in end view. 



(e) Study in like manner the slimy coating upon dead leaves 

 and twugs in water in the summer for diatoms. On some of 

 these very fine markings ma}^ be found. 



(/) Here again mounted shdes of Flat Diatoms may be 

 used with profit, but it is well to study Kving specimens so as 

 to be able to observe their motihty. 



(g) For future study in the laboratory the Conjugate Algae 

 should be preserved in bottles of water containing just enough 

 alcohol, glycerine, formaldehyde or carbolic acid to prevent 

 their decay. One-fourth or fifth of the first and second, one- 

 tenth of the third, and enough of the last to give a decided 

 odor, will usually do well enough. A 2 per cent, solution of 

 potassium acetate made light blue by addition of copper suljihate 

 will preserve the green color of these i)lants, if kept in the dark. 



LITERATURE OF ZYGOPHYCEAE 



0. S. West, A Treatise on the British Fresh-water Algae, Cam- 

 bridge, 1904. 



Frank S. Collins, The Green Algae of North America, Tufts 

 College, 1909. 



0. B. De Toni, Sylloge Algarum, Vol. II, Padua 1S91-1S94. 



H. Van Heurck. ^l Treatise on the Diatomaccac (Engl, trans.), 

 London, 1896. 



