involved root nodule microorganisms were fungi. Hellriegel and Wilfarth found
value in observation that the nitrogen gain in the soil was almost exclusively in the
form of organic compounds. They also believed that subsequently studying either
some bacteria or fungal hyphae contained within those root nodules would lead to
clarification as to how microbial behavior participated in the process of nitrogen
uptake by the legumes.
The understanding by Hellriegel and Wilfarth regarding symbiosis was of a
conceptual relationship in which two creatures exert a mutually beneficial influence
on their life’s activities. They presumed that the legumes have an ability to enter into
a symbiotic relationship with certain types of fungi as represented by the root
nodules. Hellriegel and Wilfarth assumed that their observed ability belongs to the
legumes, but not to either the gramineae or other agricultural crops. They perceived
nothing in their studies to have indicated that the cereals were able to draw a
remarkable quantity of their required nitrogen from a source other than the soil.
We since have learned that the Poaceae and indeed most vascular plants do utilize
symbiotic microbial nitrogen fixation in the form of arbuscular mycorrhizae, as will
be discussed later in this essay. We also have since learned that the legumes form
endomycorrhiza of the vesicular-arbuscular type.
14.11.1 A Summary of the Experiments Presented in This
Publication by Hellriegel and Wilfarth
Hellriegel and Wilfarth found that when legumes were grown in non-sterilized,
nitrogen-free soil, the appearance of numerous well-formed nodules was generally
observed on the legume roots. The appearance of root nodules also went hand in
hand with vigorous growth of the plants and vigorous availability of nitrogen.
Hellriegel and Wilfarth then set up initial hypotheses which included that
legumes could directly assimilate atmospheric free nitrogen, while the barley and
oats made no use of that convenient opportunity. Another hypothesis considered was
that the legumes, unlike their other test plant species, are able to take their nitrogen
from the deeper layers of the subsoil. Experimentally, they eliminated that latter
hypothesis by growing legume plants in the absence of subsoil.
Hellriegel and Wilfarth used chemically washed, thermally dry sterilized, quartz
sand to culture barley, oats, and peas. They also grew summer turnip, white mustard,
red clover, buckwheat, yellow lupine (Lupinus luteus, European yellow lupine),
serradella (Ornithopus sativus), vetch and horse bean. The dry sand sometimes was
amended with calcium carbonate, and the sand was moistened with a nutrient
solution containing potassium monophosphate, potassium chloride, magnesium
sulphate, plus sometimes sodium chloride and calcium nitrate. The plants then
were supplied with distilled water. When the gramineae and legumes were grown
under identical conditions, but without addition of nitrates, legumes growing in the
washed sand often were able to develop normally while the Gramineae remained
226
C. J. Hurst
value in observation that the nitrogen gain in the soil was almost exclusively in the
form of organic compounds. They also believed that subsequently studying either
some bacteria or fungal hyphae contained within those root nodules would lead to
clarification as to how microbial behavior participated in the process of nitrogen
uptake by the legumes.
The understanding by Hellriegel and Wilfarth regarding symbiosis was of a
conceptual relationship in which two creatures exert a mutually beneficial influence
on their life’s activities. They presumed that the legumes have an ability to enter into
a symbiotic relationship with certain types of fungi as represented by the root
nodules. Hellriegel and Wilfarth assumed that their observed ability belongs to the
legumes, but not to either the gramineae or other agricultural crops. They perceived
nothing in their studies to have indicated that the cereals were able to draw a
remarkable quantity of their required nitrogen from a source other than the soil.
We since have learned that the Poaceae and indeed most vascular plants do utilize
symbiotic microbial nitrogen fixation in the form of arbuscular mycorrhizae, as will
be discussed later in this essay. We also have since learned that the legumes form
endomycorrhiza of the vesicular-arbuscular type.
14.11.1 A Summary of the Experiments Presented in This
Publication by Hellriegel and Wilfarth
Hellriegel and Wilfarth found that when legumes were grown in non-sterilized,
nitrogen-free soil, the appearance of numerous well-formed nodules was generally
observed on the legume roots. The appearance of root nodules also went hand in
hand with vigorous growth of the plants and vigorous availability of nitrogen.
Hellriegel and Wilfarth then set up initial hypotheses which included that
legumes could directly assimilate atmospheric free nitrogen, while the barley and
oats made no use of that convenient opportunity. Another hypothesis considered was
that the legumes, unlike their other test plant species, are able to take their nitrogen
from the deeper layers of the subsoil. Experimentally, they eliminated that latter
hypothesis by growing legume plants in the absence of subsoil.
Hellriegel and Wilfarth used chemically washed, thermally dry sterilized, quartz
sand to culture barley, oats, and peas. They also grew summer turnip, white mustard,
red clover, buckwheat, yellow lupine (Lupinus luteus, European yellow lupine),
serradella (Ornithopus sativus), vetch and horse bean. The dry sand sometimes was
amended with calcium carbonate, and the sand was moistened with a nutrient
solution containing potassium monophosphate, potassium chloride, magnesium
sulphate, plus sometimes sodium chloride and calcium nitrate. The plants then
were supplied with distilled water. When the gramineae and legumes were grown
under identical conditions, but without addition of nitrates, legumes growing in the
washed sand often were able to develop normally while the Gramineae remained
226
C. J. Hurst