Rhizobia
Soybean roots contain (a) nitrogen-fixing nodules. Cells within the nodules are infected with Bradyrhyzobium japonicum, a rhizobia or "root-loving" bacterium. The bacteria are encased in (b) vesicles inside the cell, as can be seen in this transmission electron micrograph.
Source
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"OpenStax College, Nutritional Adaptations of Plants. October 17, 2013."
http://cnx.org/content/m44718/latest/Figure_31_03_02ab.jpg
OpenStax CNX
CC BY 3.0.
