82 SECRETS OF ANIMAL LIFE 



meadows." On the Beagle voyage Darwin was 

 impressed off the coast of South America with vast 

 tracts of water discolored by the minute floating 

 Algae, the " sea-sawdust " of Captain Cook's sailors, 

 and since the days of the Challenger information in 

 regard to the Phyto-plankton has grown apace. It 

 seems to be the food of many open-sea animals, 

 such as small Crustaceans, which again are devoured 

 by young fishes. The growth of the sea-meadows 

 in spring is thus as important as the garment of 

 green on the farmer's fields. Professor Herdman 

 of Liverpool, a leading authority on the biology of 

 the sea, cites the calculation that a Diatom " less 

 than the head of a pin, dividing into two at the 

 normal rate of five times in the day, would at the 

 end of a month form a mass of living matter a 

 million times as big as the sun. The destruction 

 that keeps such a rate of reproduction in check 

 must be equally astonishing." It should be 

 noticed, however, that considerable evidence is 

 accumulating in support of the view that the 

 minute constituents of the Phyto-plankton are even 

 more important in their death than in their life. 

 For when they are killed by changes of temperature 

 and the like, or when they reach the end of their 

 natural tether, they add to the valuable organic 

 detritus which remains in suspension in the water 

 or sinks to the floor of the sea. To this accumula- 

 tion of organic debris very important contributions 

 are also made from the littoral belt of seaweed and 

 sea-grass. Indeed, recent investigations by two 



