Root Nodule Formation as Affected by Planting of Shelled or Unshelled Seeds of Bur Clovers, Black Medic, Hubam, and Crimson and Subterranean Clovers 1

The purpose of these experiments was to learn whether artificial inoculation might have more prompt or intense effects when the inoculum was applied to the relatively bulky pods of the unshelled seeds than to the smaller and smoother surfaces of the shelled seeds. The experiments were made on fields of the Experiment Station Farm and of other farms near Auburn in 1926, 1928, 1930, and 1933. The sandy soils utilized were in the Norfolk series and showed acid reactions. Except as noted for one garden soil, these soils lacked the appropriate strain of nitrogen-fixing bacteria. The planting dates were usually late, or after the soil temperatures had fallen considerably below those prevailing at the optimum time for planting seed of such legumes. To avoid the usual slower germination of the bur clovers when planted in the bur, the unshelled seeds of all bur clovers were briefly scalded in water, near the boiling point, after which the inoculum was applied. The seed were inoculated by separately soaking both the shelled and unshelled (pod inclosed) seed in a suspension of appropriate cultures. This study was limited, in most of these experiments, to such effects as might be manifested by the seedlings in their earlier stages of growth through possible differentiation in the formation of root nodules. During the early life of the seedlings, frequent examinations were made to determine the percentage of plants bearing nodules, and in certain experiments, to ascertain the average number of nodules per plant. The age of the seedlings at each date of examination was reckoned from the date of emergence. The study included two species of bur clover (Med-icago arabica and M. rigidula), black medic (M. lupulina), hubam (Melilotus alba annua), crimson clover (Trifotium incarnatum), and subterranean clover (T. subterraneum).