Some Effects of ‘Hardening’ Carrot Seed

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Abstract
Carrot seed and water were mixed in the ratio of 100 : 70 by weight, kept in a covered petri-dish for 24 h at 20 °C and then dried by exposure to the atmosphere at 20 °C. Three cycles of this ‘hardening’ treatment gave seed having embryos 51 per cent longer than those in untreated seed. This increase in embryo length was due mainly to cell division during hardening rather than to cell expansion. Hardened seed imbibed water more quickly to start with and germinated and produced seedlings which emerged in the field 3–4 days earlier than untreated seed. Relative growth-rates during early growth were similar from both types of seed. At harvests 14 to 21 weeks after sowing the mean yields of roots from the hardened seed was 64.0 compared to 59.2 tons per hectare from the untreated seed. Variations of the hardening treatment were tried but it appeared that the above treatment was the most effective for enhancing the rate of germination, although embryo length and numbers of cells per embryo increased progressively with cycles of hardening up to six cycles. The moisture content of seed ripening in a field at Wellesbourne fluctuated diurnally over the same range as that used in the experiments to produce a hardening effect, but the embryos did not increase in length during field ripening.

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