Seaweeds and Leaf-green 
Such diatoms, even if they do escape the codfish, 
have not necessarily wasted their lives. Each minute 
cell contains a drop of oil, and such oil-drops accumu- 
lating in the muddy deposits may become infinitely 
valuable stores of petroleum. 
“Chocolate creams” and “wax” candles made from 
them may be very useful and agreeable after a few more 
geological zeons. 
Almost as numerous sometimes are those very strange 
coccoliths which are also unicellular plants of the high 
seas. Their curious arms are possibly an attempt to 
defend themselves from minute enemies of some kind. In 
one sample of globigerina ooze, 68 per cent. of its weight 
and 71 per cent. of its volume consisted of coccoliths ! 
Sometimes ona gloomy and quiet night, when the sea is 
a dark indigo-blue, one notices a very strange pheno- 
menon. As the vessel’s prow breaks the still dark water, 
the curling wavelets sparkle with faint lights for a second 
or two. Itis especially well seen in the wake churned by 
the propellers, which is touched up with the faint phos- 
phorescence for quite a long time. But every little 
ripple, as it breaks gently, is spangled with the same 
tiny sparks which one sees appearing and vanishing all 
over the surface. 
These lights are generally due to a minute alga 
(Pyrocystis noctiluca), which, though small, is a very 
giant amongst its allies, for the single cell is from half to 
one millimetre long (.01968 to .03937 inch). There are 
many other phosphorescent plants and even animals, 
They must be sometimes present in enormous numbers. 
Near Florida Dr. Schiitt estimated that there was a 
population of 50,000 in one square mile. 
The spark is of distinct use to it, for when a pyrocystis 
sees that it is in danger of being gobbled up by some 
minute crustacean copepod, it gives out its tiny light 
38 
