Germination of
Hibiscus seeds, especially in perennial species, is usually very slow and insufficient due to the high percentages of hard grains. Artificial promotion of seed germination by H
2SO
4 treatment proved satisfactory (TACHIBANA et al. 1957). In this paper, further examinations of the method are presented in some detail.
1. Six species, including an unidentified species from Nepal Himalaya (collected by S. NAKAO in 1953), were newly examined with respect to the characteristics of their seed germination. Germination test of untreated seeds generally resulted in low germination rate, but the promoting effect of H
2SO
4 treatment was remarkable in all of the species. According to the classification proposed in the preceding paper(TACHIBANA et al. 1957), they were included in the following categories.
Germination of untreated seeds
Germination of seeds treated with H
2SO
4 acetosella Group III Group Ill Himalaya 665 N N Mallow Marvels N Ill
militaris VI III
gossypinus N Ill
peduculatus N N It was noticed that the seeds of certain uncultivated annual species such as Himalaya 665,
gossypinus, acetosella, Trianum etc. contained many hard grains while most of the annual species in cultivation produce few hard seeds.
2. Germination of treated seeds was accelerated by high temperature during incubation, but no significant interaction existed between the temperature and the duration of H
2SO
4 treatment(Fig. 4, Table 2).
3. At 20°C, the acid solution 40% in concentration was ineffective for seeds of
H. Moscheutos. The lowest effective concentration is probably 45%. The product, [effective concentration of H
2SO
4 (actual concentration minus 45%)] × [duration of H
2SO
4 treatment in minutes], was closely correlated with the per cent germination throughout the treatments tested (Fig. 5). The correlation showed that high percentage (>70%) of germination was always assured by the range of the product 900-6, 000 (% min).
4. Using 98% H
2SO
4, the combined effect of temperature and duration of H
2SO
4 on germination of
H. Moscheutos seeds was examined. The higher the temperature during treatment, the earlier the germination percentage was reached, but the severer the damage due to longer duration of the treatment (Fig. 6). The relation between per cent germination and accumulated temperature during the treatment could be described by a single optimum curve (Fig. 7), which suggested that the treatments between 150 and 2, 000 (°C min) were most effective.
5. Relative humidity during 4 months of seed storage before germination had only a slight influence on the effect of H
2SO
4 treatment (Fig. 8).
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