v] THE SOURCES OF FOOD 133 



disappears far above that level. It is only in the 

 upper strata of the sea that plants can reproduce 

 and grow, for only there do they receive the energy 

 of sunlight necessary for the photo-synthesis of 

 carbohydrate food-stuff. It does not help them that 

 practically unlimited quantities of carbon dioxide 

 can be obtained from the atmosphere, and unlimited 

 energy from solar radiation, for their production can 

 only keep pace with the limited amount of nitrogen 

 compounds present in solution in the water. On the 

 other hand it is of no avail that more nitrogen is 

 present in the depths, for in the absence of the power 

 of photo-synthesis of starch, no proteid can be formed, 

 and unlimited nitrogenous food-stuff would be of no 

 use to them. Production goes on only in the upper 

 well-lighted layers of the sea and the dead bodies of 

 plants and animals living there fall to the sea-bottom 

 and accumulate in the oozes, the globigerina and 

 diatom deposits for instance. Now it is doubtful 

 how far bacterial life can flourish at the sea-bottom 

 where the temperature is very low, and some samples 

 of oozes examined seem to have been sterile in the 

 media employed for cultures. Some amount of 

 bacterial action may go on, but what it is exactly 

 we do not know research in this direction is urgently 

 needed. We may however conclude that the processes 

 of putrefaction proceed much more slowly at the 

 bottom of the ocean than on the land, or in shallow 



