10.1 The seeds of some species of clover (Trifolium spp.) will not germinate immediately after ripening, but must undergo a period of ‘softening’, by exposure to fluctuating high and low temperatures, usually on the soil surface. In an investigation of this phenomenon, seeds of eight clover species were sown into strips of fine mesh cotton bags, 100 seeds of a single species in each bag. Each strip comprised one bag of each species. At the start of summer, the bags were laid on the soil surface in full sun at a site cleared of vegetation.

At intervals during the summer and autumn, two or four strips were removed from the field, and the seeds in each bag were tested to determine how many were still ‘hard’ (i.e.

would not germinate when moistened in favourable conditions). The first and last few rows of the spreadsheet holding the data are presented in Table 10.10: the full data set is held in the file ‘clover seed softening.xlsx’ on this book’s website (see Preface). (Data reproduced by kind permission of Hayley Norman.)

Table 10.10 Numbers of ‘hard’ and ‘soft’ seeds of several species of clover after exposure on the soil surface for varying lengths of time.
Observations on the same replication at the same time come from a single strip of bags. Time=interval in days from the start of exposure on the soil surface. nhard=number of hard seeds in a single bag. nsoft=number of soft seeds in a single bag.
A B C D E 1 species! replication! time nhard nsoft 2 T. glomeratum 1 0 98 2 3 T. glomeratum 2 0 99 1 4 T. glomeratum 3 0 99 1 5 T. glomeratum 4 0 99 1 6 T. spumosum 1 0 94 6 7 T. spumosum 2 0 93 7 8 T. spumosum 3 0 95 5 9 T. spumosum 4 0 96 4 ⋅ ⋅
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234 T. scutatum 1 174 4 96 235 T. scutatum 2 174 11 89 236 T. scutatum 3 174 5 95 237 T. scutatum 4 174 5 95 238 T. pilulare 1 174 17 83 239 T. pilulare 2 174 28 72 240 T. pilulare 3 174 241 T. pilulare 4 174 Source: Data reproduced by kind permission of Hayley Norman.