14.11 “Untersuchungen über die Stickstoffnahrung der
Gramineen und Leguminosen” by Hermann
Hellriegel and Hermann Wilfarth, 1888
Hermann Hellriegel and Hermann Wilfarth (1888) set for themselves the goal of
developing a new hypothesis about the uptake of nitrogen by papilionaceae, which
we presently know as the subfamily Papilionoideae within the family Fabaceae. It
had been known that the growth of crop plants generally was directly related to the
amount of nitrogen added to the soil. But, that also was known to be a correlation
which did not hold true for the papilionaceae. This particular publication covered
research data from 1882 through 1887.
Hellriegel and Wilfarth had determined in 1882 and 1883 that papilionaceae
could grow well in nitrogen free soil, and similarly could grow in nitrogen-free
liquid nutrient solutions. Prior to these studies by Hellriegel and Wilfarth, the root
nodules on legume plants had long been regarded as pathogenic formations similar
to galls. Gradually, though, the notion became widespread among the scientific
community that these root nodules were normal structures belonging to the plant.
Some observers had considered the nodules to be used for assimilation of nitrogen,
while other observers believed the nodules were used for storage of nitrogen
compounds.
Hellriegel and Wilfarth included in their publication as background information
some mention of findings by other scientists. In particular, a discovery by Berthelot
(whom I might guess to have been Pierre Eugène Marcellin Berthelot) that nitrogen
becomes bound in non-sterilized soil, and the bound nitrogen then exists in a form
that cannot be washed out by water. Berthelot also had shown that a sterilized soil
does not similarly bind nitrogen. Berthelot determined this accumulation of free
atmospheric nitrogen to represent assimilation by microorganisms that were present
in the soil, and that the assimilated nitrogen was deposited in the form of protein
substances. Berthelot presumed this nitrogen fixation was due to the activity of
bacteria which existed in the soil, albeit proof that this process of nitrogen binding
was due to the activity of bacteria had not yet been obtained.
Hellriegel and Wilfarth also understood that part of the nitrogen present in soil
existed as complex organic compounds such as plant residues and humus substances
which are converted into ammonia, and they attributed that knowledge to
Boussingault (whom I might guess to have been Jean-Baptiste Boussingault).
Jean-Baptiste Boussingault additionally has been credited as identifying the basic
idea of the biological nitrogen cycle by demonstrating that plants do not absorb
nitrogen as an element from the air, but rather plants obtain nitrogen from soil in the
form of nitrates.
Hellriegel and Wilfarth cited Albert Bernhard Frank as having concluded from
his own work that the process of binding nitrogen into soil compounds is favored by
the presence of living plants. Hellriegel and Wilfarth mentioned that while another
opinion existed, which was for the necessary nitrogen simply to be absorbed from air
by moist soil, that opinion clearly could not explain why absorption of the necessary
224
C. J. Hurst
Gramineen und Leguminosen” by Hermann
Hellriegel and Hermann Wilfarth, 1888
Hermann Hellriegel and Hermann Wilfarth (1888) set for themselves the goal of
developing a new hypothesis about the uptake of nitrogen by papilionaceae, which
we presently know as the subfamily Papilionoideae within the family Fabaceae. It
had been known that the growth of crop plants generally was directly related to the
amount of nitrogen added to the soil. But, that also was known to be a correlation
which did not hold true for the papilionaceae. This particular publication covered
research data from 1882 through 1887.
Hellriegel and Wilfarth had determined in 1882 and 1883 that papilionaceae
could grow well in nitrogen free soil, and similarly could grow in nitrogen-free
liquid nutrient solutions. Prior to these studies by Hellriegel and Wilfarth, the root
nodules on legume plants had long been regarded as pathogenic formations similar
to galls. Gradually, though, the notion became widespread among the scientific
community that these root nodules were normal structures belonging to the plant.
Some observers had considered the nodules to be used for assimilation of nitrogen,
while other observers believed the nodules were used for storage of nitrogen
compounds.
Hellriegel and Wilfarth included in their publication as background information
some mention of findings by other scientists. In particular, a discovery by Berthelot
(whom I might guess to have been Pierre Eugène Marcellin Berthelot) that nitrogen
becomes bound in non-sterilized soil, and the bound nitrogen then exists in a form
that cannot be washed out by water. Berthelot also had shown that a sterilized soil
does not similarly bind nitrogen. Berthelot determined this accumulation of free
atmospheric nitrogen to represent assimilation by microorganisms that were present
in the soil, and that the assimilated nitrogen was deposited in the form of protein
substances. Berthelot presumed this nitrogen fixation was due to the activity of
bacteria which existed in the soil, albeit proof that this process of nitrogen binding
was due to the activity of bacteria had not yet been obtained.
Hellriegel and Wilfarth also understood that part of the nitrogen present in soil
existed as complex organic compounds such as plant residues and humus substances
which are converted into ammonia, and they attributed that knowledge to
Boussingault (whom I might guess to have been Jean-Baptiste Boussingault).
Jean-Baptiste Boussingault additionally has been credited as identifying the basic
idea of the biological nitrogen cycle by demonstrating that plants do not absorb
nitrogen as an element from the air, but rather plants obtain nitrogen from soil in the
form of nitrates.
Hellriegel and Wilfarth cited Albert Bernhard Frank as having concluded from
his own work that the process of binding nitrogen into soil compounds is favored by
the presence of living plants. Hellriegel and Wilfarth mentioned that while another
opinion existed, which was for the necessary nitrogen simply to be absorbed from air
by moist soil, that opinion clearly could not explain why absorption of the necessary
224
C. J. Hurst