HOW TO KNOW THE FRESH-WATER ALGAE 



light. A small quantity of red or 'bloody' snow when allowed to melt 

 in a jar may yield a surprising quantity of this and other genera 

 such as ScofieiJa, Ankistrodesmus, and certain Dinoflagellates. 



Specimens collected 

 from the open water 

 (planktonic algae) are 

 best collected with a 

 cone-shaped, silk, bolt- 

 ing cloth net (No. 20). 

 Plankton nets are ob- 

 tainable from biologi- 

 cal supply houses, or 

 may be made up by 

 securing a yard of the 

 silk from an importer 

 or from a flour mill. 



THE PLANKTON NET 



(The Limnological and Oceanographic Society of America publishes 

 a list of commercial houses and firms where various kinds of col- 

 lecting equipment may be obtained.) A light-weight, brass (preferred) 

 or thin galvanized iron ring (stout wire), or band may be used for the 

 mouth of the net. A convenient size is a ring about 6 or 8 inches in 

 diameter. Using a pattern, (see Welch, P. S. 1948. Limnological 

 Methods, Blakiston Co., p. 234-235) cut the silk so that when attached 

 to the ring a cone about 14 inches long is formed. The silk should 

 not be attached directly to the ring, but sewed first to a band of stout 

 muslin which then may be sewed over the ring or metal band. If a 

 flat band is used for the mouth of the net the edges should be filed 

 smooth and rounded to eliminate as much cutting and fraying of the 

 muslin cloth as possible. The net may be used as a closed cone, in 

 which case after a sample has been collected, the net must be turned 

 inside out and the material washed off in a dish or jar. More con- 

 veniently, the tip of the cone may be cut off at a point (about Vi in. 

 or less from the end) which will permit the insertion of a small homeo- 

 pathic vial (4 to 6 dram capacity) which can be tied about its neck 

 into the apex of the net. Thus the sample will become concentrated 

 in the vial and when the net is reversed the material can be poured 

 out into a collecting bottle, and the net rinsed before another sample 

 is taken. Better still, a small metal (lightweight) band, threaded to 

 receive a screw-cap vial neck can be sewed into the tip of the net. 

 Then the vial can be simply unscrewed and a fresh one inserted after 

 the net has been rinsed. 



The net should have 3 leaders of equal length attached to the 

 ring at regularly spaced points. The leaders should be tied to a 

 small ring to which the tow cord is also attached. Use a heavy line 



14 



