496 LIFE IN THE OCEAN. 



certain plants with certain sorts of bacteria. It is leguminous plants 

 alone, and of leouniinous plants onh^ those upon whose nodes certain 

 bacteria live, that can tix the atmospheric nitrogen and use it to make 

 all)umen. In the absence of the specific bacteria the leguminous plants 

 lose this property and behave like other plants, as can he seen by 

 cultivating them in sterilized soil. In respect to compensation for 

 losses of nitrogen, the intimate union between leguminous plants and 

 certain bacteria is prol)a))ly of fur more importance than the fixation 

 of nitrogen by atmospheric electricity. 



As far as we know, the cycle whose essential steps have just been 

 sketched is performed in the sea as on the land. In water, as on land, 

 plants alone furnish the food; l)ut, since thev can not produce organic 

 matter without light. th(\v grow only in the upi)er strata of the ocean, 

 down to a depth of scmie hundreds of meters. The marine plantsare, 

 moreover, ecjually subject to t\w law of the minimum. The analysis 

 of the medium in which they live — that is to sa}'. of the water with 

 the solid and gaseous substances that it holds in solution — will permit 

 the formation of conclusions analogous to those that soil analysis 

 suggests for terrestrial plants. Aloreover^ as well as we can judge 

 from recent observations, nitrifying and denitrifying bacteria pla}'' 

 important parts both in fresh water and in the ocean. 



The three nitrogen compounds of Avhich we have spoken, together 

 with all their salts, are particiUarly soluble, and, consequently, rains 

 carry ofi' a part of the compounds of this kind. The water thus 

 charged with anmionia and nitric acid flows ofi' by the ditches and 

 brooks to the ponds, lakes, and water courses, and ultimately reaches 

 the sea. The land is, in that way, continually being robbed of a cer- 

 tain quantity of nitrogen compounds, to the profit of the sea. The 

 loss thus sustained by the soil is made up by the formation of new 

 (juantities of nitrogen compounds, due in small part to the action of 

 storms, but, probably, chieflv by the intervention of bacteria living in 

 the nodes of leguminous plants. 



One naturally expects to find in the sea an animal and vegetable life 

 far more intense than on land, for the reason that the sea, in the course 

 of time, must have been extraordinarily enriched with nitrogenous 

 substances. Indeed, it seems that the incessant bringing of such sub- 

 stances ought, after some hundred thousands or millions of years, to 

 have poisoned the sea and rendered life there quite impossible. Yet, 

 in point of fact, we neither find that life in thejocean has been cut off, 

 nor do we meet there an}'^ very extraordinary wealth of living organ- 

 isms or of nitrogen compounds. On the contrary, the few observa- 

 tions made enable us to declare that sea water does not contain, so 

 much combined nitrogen as earth does. This apparent contradiction 

 mav, in the present imperfect state of our knowledge, be supposed to 

 be explicable by the action of denitrifying bacteria. From this point 



