BOTANY. 291 
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. 
Special attention in Polar waters should be paid to discoloured 
water and ice. The former should always be carefully tow-netted ; 
and the latter thawed and filtered. Enormous shoals of marine 
Diatoms in the Antarctic have been recorded by Sir Joseph Hooker, 
the Challenger expedition, etc., and associated with these, dia- _ 
tomaceous oozes of great extent on the bottom. 
Minute fresh-water Algz are well preserved in carbolic acid 
(about 1 per cent.), or in camphor water, or weak spirit where these 
are not to be obtained. Submerged plants 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 pools, and of swampy places 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. 
The bottles when taken home should be well shaken, the contents 
poured into filtering-paper, left to dry, and folded up as they are, 
labelled with locality, approximate height above sea-level, date, and 
character of the water, whether fresh, brackish, cold or thermal. 
Water-weeds, Sphagna, etc., growing in lakes and pools, should 
be gathered, washed, and gently squeezed in water, and the sediment 
u 2 
