1978 



Journal of Applied Microscopy 



At this point nitrification is demonstrated by means of the flasks prepared 

 beforehand. Small portions of all three flasks are tested in tubes for ammonia 

 and nitrites, and in watch glasses for nitrates ; the differences between them 



being pointed out, and ex- 

 planations given as to how the 

 flasks were treated. The photo- 

 graph (Fig. 3) shows: 1. Con- 

 trol. 'I. Nitrosification. 3. The 

 nitrites all oxidized to nitrates. 

 " Now green plants, speaking 

 generally, can only utilize nitro- 

 gen when it is in the form of 

 nitrates, so in this way the cycle 

 of life is completed. 



But on the way round there 

 is considerable loss of nitrogen ; 

 much passes off as free N during 

 the reduction of soluble matter to 

 ammonia, and the same occurs to 

 a great extent by the action of 

 the denitrifiers. All the nitrogen 

 therefore does not come back to 

 the green plants in the form of 

 nitrates and this loss must be 

 made up somehow. Plants, 



Fig. :). — Center. — Nitrite Reaction with (iriess-Ilovsay 

 Solution. Left and Right. — No Reaction. 



animals, and bacteria we have so far 

 considered can use and waste nitrogen, 

 but they cannot fix it from the air. 

 Nor is there in nature any fixation of 

 nitrogen by chemical processes — or at 

 least only to a very limited extent. 



There is, however, a class of bac- 

 teria which can fix free N from the air 

 under special circumstances, and hand 

 on their nitrogenous surplus products 

 to be utilized by certain green plants, 

 — the leguminosae, among which are 

 peas, beans, clover, locust trees, etc. 

 These bacteria are called nitrogen 

 fixers and are universally present in 

 the soil. 



The seed of a leguminous plant 

 when sown contains enough nitrogen 

 to start the young plant growing. The 

 stem shoots up a little way and the 

 rootlets penetrate the soil to a consid- 



B'T NITROCCN riXERS 

 I 

 L t C U M I N L/ i 



NON LCCUM INOUS 



NITRITES TO 



AMMONIA TO NITRiTf^ 



NSOLUBLE ORSANIC TO 

 SOLUBLE BY 



AN^ROB/CS 



SOLUBLE ORCAMIC TO 

 AMMONIA Br FACULTATIVES OR 

 AN/C ROB ICS 



1 



a; 



Fig 4. 



