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Observations on the Root Nodules of Purshia tridentata

G. Bond
Proceedings of the Royal Society of London. Series B, Biological Sciences
Vol. 193, No. 1111 (Apr. 13, 1976), pp. 127-135
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/77115
Page Count: 11
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Observations on the Root Nodules of Purshia tridentata
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Abstract

Purshia tridentata, an important browse plant in arid regions of western U.S.A., is one of the few members of the Rosaceae that are known to bear root nodules. Except for some evidence that they are nitrogen-fixing the nodules of P. tridentata have been little studied. In the present work nodulated plants of the species have been found to grow satisfactorily in nitrogen-free water culture and to fix up to 40 mg nitrogen per plant, by inference in the nodules, during the 16 months from seed sowing. Acetylene assays confirmed that nitrogenase activity was shown by the nodules but not by the roots. These findings add to the evidence obtained by previous workers for the occurrence of fixation in the nodules. The assessment of the ecological importance of the fixation is hindered by lack of information on the regularity of nodulation in the species in its natural habitats. A study of the nodules under the light and the electron microscope showed that their general structure resembles that of other non-leguminous nodules, especially those of Dryas, and that the endophyte consists of septate, branching hyphae about 0.5 μ m wide which produce vesicles (not internally sub-divided) and 'bacteria-like' cells. Thus the endophyte resembles the micro-organisms found in other non-leguminous nodules and commonly regarded as closely allied to the actinomycetes.

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