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The pattern of nodule formation (time of formation, number, distribution, and size) was examined in 15 varieties of subterranean clover and in some autotetraploid and hybrid lines, with the following results: (1) The time at which nodules first appeared on the seedling differed significantly between varieties by 2-3 days but was not affected by ploidy. (2) Selection in hybrids for early- or late-nodulating habit beyond parental limit failed, except in the cross Tallarook x Morocco, which segregated dwarfs that nodulated late. Except in this cross, the time at which nodules first formed was inherited polygenetically. (3) Bacterial strains differed (by several days) in the time at which they initiated nodulation; strain and host differences were generally independent. (4) The average number of nodules formed differed up to sixfold between varieties; autotetraploids formed 32% fewer nodules than diploids. Differences between individual plants of one variety were small. (5) The habit of abundant nodule formation in hybrids was dominant over sparse nodulation, and in the F |
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