182 THE MICROSCOPE. 



COLLECTING ALGyE AND DESMIDS. 



By Dr. ALFRED C. STOKES, 



TRENTON, N. J. 

 [From Introduction to Keys to Fresh- Water Algae.] 



Alga? and Desmids are singly invisible to the naked eye. It 

 is only when they occur in large masses that the eye can take 

 cognizance of them. It rarely occurs, however, that the Des- 

 mids are so abundantly congregated that they thus obtrude 

 themselves on the observer. When a large quantity has been 

 collected and the vessel placed near a window, they will collect 

 in a green film at the surface of the water on the lighted side, 

 and there become visible in mass. In the ponds and shallow? 

 such an occurence is not common. At times they are found so 

 abundantly that by holding a glass vessel of the water up to the 

 light they may be seen floating about as minute green objects, 

 which the trained eye will recognize and the pocket lens make 

 distinct. But these varieties are among the largest of the forms- 

 according to my experience they are always exclusively con- 

 fined to the Closteriums. Other large forms, like Micrasterias, 

 at least in the writer's locality, rarely occur in such profusion. 

 To collect the Desmids, therefore, it is necessary to collect by 

 faith. The microscopist can know exactly what he has only 

 when he gets home and examines the water drop by drop un- 

 der the microscope. 



'With the Algse it is different. These are usually visible to 

 the naked eye, as they are almost invariably collected in large 

 masses floating on the surface, submerged just beneath the sur- 

 face, or attached in waving tufts or fringes to sticks and stones 

 and other plants in the ponds. The e} T e of faith is not needed 

 to recognize them. They usually force themselves on the wond- 

 ering attention of the observing pedestrian in the wayside lanes, 

 beside the ditches and slow brooks. As soft emerald clouds, or 

 graceful streamers floating in the sluggish current, or resting 

 like a green scum on the surface, they are readily seen and as 

 easily gathered. No collecting tools are demanded for either 

 Algse or Desmids, except a dipper of some kind, a common tin 

 dipper is as good as anythig, and a few bottles or other vessels 

 to carry the treasures home, and to keep them concealed from 

 inquisitive people ; the collecting naturalist must always be pre- 

 pared for a meeting with such persons. 



