344 NOTES AND COMMENTS [may 



the ambitious plankton statistics of Hensen and his colleagues are 

 two widely separate instances of the many-sided attack which is being- 

 made on the problems of " Stoffwechsel " in aquatic life. 



In his address, Professor Brandt has naturally much to say 

 concerning nitrogen, and, at the risk of being trite, we may summarise 

 his general argument, so that the point of his final suggestion may be 

 made clear. The sources of nitrogen available for plant -life are 

 nitrates, nitrites, and ammonia, to which must be added the nitrogen 

 of the atmosphere in so far as that may be brought into available 

 form by electric discharges and by help of the symbiotic fungi in the 

 root-tubercles of Leguminosae. From these simple raw materials the 

 plants elaborate the albuminoids which form the fundamental nitrogenous 

 supplies of animal life. On the death of the animals part of the 

 nitrogenous material becomes by putrefaction again available as food 

 for plants. Bacteria affect the circulation in two ways : — on the one 

 hand, over the whole earth there are nitrifying bacteria by help of 

 which ammonia becomes the origin of nitrites and nitrates ; on the 

 other hand, there are denitrifying bacteria which effect the reduction 

 of nitrates and nitrites, so that ammonia results, and also some free 

 nitrogen which passes out of the circle of life. So it is in dry land, 

 and so in the sea. Plants raise inorganic substances to an organic 

 level ; animals feed upon and return food to plants ; and bacteria affect 

 the circulation of matter in two directly opposite ways. The land is 

 always losing nitrogenous substances to the sea, and the only known ways 

 in which the land is compensated for its loss are by electric discharges 

 in the atmosphere and by the root-tubercles. This consideration sug- 

 gests at first sight a possible poisoning of the sea with nitrogenous 

 substances in the course of millions of years ; but the suggestion is 

 probably fallacious, since it ignores the action of the denitrifying 

 marine bacteria which destroy any superfluity of nitrogenous com- 

 pounds in the water, and thus tend to preserve the balance of nature. 



After expounding Hensen's plankton-method, to which he attaches 

 great importance as affording a sure statistical basis for physiological 

 conclusions, Brandt discusses two results which are of much interest. 

 The first is, that on the whole the shallow seas are richer in plankton 

 than the deep areas, of which the Sargasso sea, for instance, may be 

 cited as a very sparsely peopled area. The explanation of this is to 

 be found in Liebig's law, that there must be a minimum of each of 

 the eleven or twelve essential chemical elements present if plants are 

 to thrive. In the shallow seas this minimum is secure, for the land 

 is nearer and the area of distribution less vast ; in the deep seas the 

 material is so much more widely distributed that the nutritive medium 

 becomes, so to speak, too thin. Apstein has shown that the quantity 

 of pelagic life in lakes varies in direct proportion to the quantity of 

 nitrates present. The second conclusion — perhaps the most striking 

 which has yet resulted from plankton studies — is that the tropical and 



