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 aeons. 



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 on a gloomy and quiet night, when the sea is 

 a dark indigo-blue, one notices a very sti-ange pheno- 

 menon. As the vessel's prow breaks the still dark water, 

 the curling wavelets sparkle with faint lights for a second 

 or two. It is 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. SchUtt 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 



