ATTEMPTS TO DEMONSTRATESYMBIOTIC NITROGEN‐FIXING BACTERIA WITHIN THE TISSUES OF CASSIA TORA

Abstract

From the standpoint of soil fertility the leguminous plants have for a long time maintained an exceptional position because of their symbiotic relationship with nitrogen-fixing bacteria. This symbiosis between plant and microorganism is commonly recognized by the visible manifestation of nodules on the root systems of these plants. Members of the sub-family Papilionatae are among the most common examples. Fewer data on the presence of nodules in the sub-families Mimosoideae and Caesalpinioideae are available, probably because their members are trees, shrubs or plants distinctly unsuitable as field crops. Of twenty-four members of the Mimosoideae cited by Leonard (9) only one, Acacia Baileyana F. Muel., lacked nodules, whereas twenty members of the Caesalpinioideae, also cited by Leonard, were found by various investigators to lack nodules. Chamaechrista nictitans (L.) Moench., Chamaechrista fasciculata (Michx.) Greene and Chamaechrista Simpsoni Pollard were exceptions. It has often been suggested that the absence of nodules on various leguminous plants does not necessarily preclude the presence of nitrogen-fixing bacteria within the root tissue. For several reasons this question has never been thoroughly investigated. Joshi (7) was probably the first to suggest that root nodule bacteria existed in the root tissues of certain papilionaceous plants although root nodules were not formed. He proposed this explanation for the substantial increases in yield and high nitrogen contents which were obtained in the culture of these plants. Joshi further conjectured that such a condition might occur due either to a lower virulence of the specific organism or to a slower reaction of the plant to the stimulus of the organismal attack. His histological studies failed to show the presence of any organisms in the root tissues. It is now obvious that some of his results can be explained on a cross-inoculation basis. Feher and Bokor (5) and Friesner (6) have also proposed the idea that root nodule bacteria might benefit plant growth without forming nodules. Critical examination of the above papers is difficult since the techniques were not satisfactorily described. On the basis of Joshi's paper one might