The Micro-uiyanisms of the Soil. 
849 
oxygen. It does not necessarily occur in all cases, or may not be 
observed owing to a reverse concomitant process, i.e. the fixation of 
nitrogen. Nitrogen losses can be expected during decay, on account 
of the action of the produced nitrous acid upon the amide-like disso- 
ciation of humous bodies, as well as in the formation of easily dis- 
sociable ammonium nitrites. A peculiar case of the disappearance 
of available nitrogen exists in the reduction of nitrates, as noticed 
by the author, by Gayon and Dupetit, and by Deherain and 
Marquenne. 
Organisms by whose Activity the Soil is Enriched in 
Nitrogen. 
A distinction must be drawn between the liigher and lower 
plants. It is a well-known fact that most plants cannot assimilate 
free nitrogen ; whereas there are sound reasons for the belief that 
leguminous plants * are exceptions to this rule. The explanation 
has been sought in the root-nodules.^ These nodules contain a 
tissue, consisting of thin-walled cells filled with an albuminous 
substance, consequently they are richer in nitrogen than the roots ; 
they have been regarded by some as pathogenic (i.e. disease-pro- 
ducing) growths, by others as reserve stores for albumin. We may 
now conscientiously assume that these nodules arise through exterior 
infection, and that they are not normal growths. 
Hellriegel and Wilfarth, in their great work upon this subject, 
state : — “ The leguminous plants deport themselves quite differently 
from the non-leguminous plants respecting the assimilation of nitro- 
gen, the latter being totally dependent for their nitrogen needs upon 
the nitrogen compounds present in the soil, and their development 
being proportional to such disposable supply. The leguminous plants 
have, besides the soil nitrogen, a second source from which they can 
abundantly cover any deficiency existing in the first. This second 
source is free atmospheric nitrogen. The leguminous plants attain 
this power by the co-operation of active living micro-organisms. 
The mere presence of low organisms in the soil does not suffice to 
make the free nitrogen serviceable, but it is necessary that certain 
kinds of organisms enter into a symbiotic relationship with the 
leguminous plants.” 
Lupins acquire nitrogen like the other leguminous plants. They 
starve in a soil free from nitrogen, when the presence of low 
organisms is excluded ; but when this is not the case their growth 
' “ Legumes ” is the word used the author, but inasmuch as this is the 
French word for “ vegetables,” whilst in England the word legume is used to 
denote the fruit (the pod) of beans, peas, vetches, clover, &c., it has been 
deemed expedient to speak of “ leguminous plants ” throughout, so as to avoid 
confusion or misunderstanding. — E d. 
^ “ Tubercles ” is the word used by the author, but as it is suggestive of 
the disease termed tuberculosis in animals, the less objectionable word 
“ nodules ” — employed in the Kothamsted memoirs — has been substituted in 
every case. — E d. 
