In order to clarify the cause of the poor seed formation in Saijo Japanese persimmon, the development of its ovules was histologically examined as compared with that of Fuyu having the strong ability in the seed formation. Further, the pollen germination and pollen tube elongation on the agar media containing diffusates from style and ovary were investigated in the 2 cultivars. Pollens used for the test were obtained from Zenjimaru, a typical cultivar of pollinizer for them.
1. The longitudinal ovule diameter in Saijo was about half as much as in Fuyu 25 to 20 days before bloom. However, the growth of ovules 10 days before bloom to blooming time, was rapid in Saijo as compared with that in Fuyu.
2. Each of nucellus, inner integument and outer one already initiated the differentiation 25 to 20 days before bloom in both of Saijo and Fuyu. Since then, the 2 cultivars were similar in the time course of embryo development, i. e., embryo mother cells were formed in the portion of nucellus 18 to 13 days before bloom, and normal embryo sac with an egg cell, 2 synergid cells, 3 antipodal cells and 2 polar nuclei was completed 4 to 3 days before bloom.
3. The rate of abnormal ovules with non-differentiated egg cells and polar nuclei surveyed at blooming time was higher in Saijo(45.5%) than in Fuyu(33.3%).
4. The obvious differences between the 2 cultivars were not observed in the rates of pollen germination on agar media containing diffusates from style and ovary. The elongation of pollen tubes, however, was found to be inhibited more in Saijo than in Fuyu by the diffusates from these tissues 12 hrs after the pollens were sown on the media.