130 DIRECTIONS FOR COLLECTING 



chromic acid 0*25 per cent, solution or platinic chloride 0*5 per cent, 

 solution is excellent as a fixing and preserving fluid ; but where 

 minute calcareous organisms are involved, f(>rmalin (5 per cent.) 

 gives good results for them as well as for all the other kinds, and 

 is to be recommended for general use. 



Minute fresh -water Algae are well preserved in carbolic acid 

 (about 1 per cent.), or in camphor water, or weak spirit where these 

 are not to be obtained. Such submerged plants as Myriophylluia^ 

 Utricularia^ Nyiwphma, Nwphar^ and Xitella should be squeezed, and 

 after the water has stood for some time the upper part may be 

 decanted and the sediment preserved. Scrapings from moist and 

 dripping rocks yield good results. 



To the special collector of Diatoms some directions may be given in 

 addition to what has l:)een said above. 



Diatoms. 



The mud of lakes, pools, and backwaters of rivers, and of swampy 

 places on moors, will repny attention. Where it looks yellow, 

 or shows the presence of Diatoms by giving off little bubbles of 

 gas, it should be scraped up by a fine muslin net attached to a 

 wire frame. The contents of the net should be turned out into a 

 pan, stirred well, and the supernatant sediment poured into a wide- 

 mouthed bottle. Repeat this until there is a good quantity in the 

 bottle, then wash the net and pan thoroughly, and try another 

 place. 



In alpine and subalpine places the surfaces of boulders in lakes 

 and streams should be scraped in the same way. These are 

 generally much purer gatherings than the muds. Perpendicular 

 rocks by the sides of streams should be scraped, and the rock-faces 

 above the surface of the water should be examined for any little 

 white tufts or patches of Diatoms which have grown there when the 

 waters were higher and liave become sun-dried. Wooden cattle- and 

 horse-troughs often yield specimens. 



The bottles when taken home should be well shaken, the contents 

 poured into filtering-paper, left to dry, and folded up as they are, 



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