LABORATORY STUDIES 183 



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

 The large lunate desmids (Closterium) are often more common. 

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

 ing rapidly. 



(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 

 early spring gathers on the top of the water of brooks, ditches, 

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

 Himdreds of Flat Diatoms may be seen moving rapidly in 

 every 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 shmy coating upon dead leaves 

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

 these very fine markings may be found. 



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

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

 to be able to observe their motility. 



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

 should be preserved in bottles of water containing just enough 

 alcohol, glycerine, formaldehyde or carboUc 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 sulphate 

 wiU preserve the green color of these plants, if kept in the dark. 



LITERATURE OF ZYGOPHYCEAE 



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

 bridge, 1904. 



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

 CoUege, 1909. 



G. B. De Toni, Sylloge Algarum, Vol. II, Padua 1891-1894. 



H. Van Heueck. A Treatise on the Diatomaceae (Engl, trans.), 

 London, 1896. 



