AND PRESERVING PLANTS. 
123 
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, formalin (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 Algse 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 Myriophyllum, 
Utricularia, Nymphma, Nuphar, and Nitella 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 been said above. 
Diatoms. 
The mud of lakes, pools, and backwaters of rivers, and of swampy 
places on moors, will repay 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 have 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, 
