Abstract
Of three species of cultivated cucurbits viz. Cucurbita Pepo Linn., C. maxima Duchesne, and C. moschata Duchesne, the last is the most popularly grown throughout Japan. Cultivation of the other two species is rather limited to the northern part. As the blooming period of C. moschata falls in the rainy season in the main growing districts in this country, very poor setting of fruit occasionally results. Accordingly artificial pollination is often of practical importance, and successful pollination is held to be secured only in the earlier part of the day.
In connexion with this point, germination tests of pollen at various ages of the flower have been made with different cultural varieties belonging to the respective species as given below.
Cucurbita maxima: Hubbard, Delicious.
C. moschata: Shishigatani, Chirimen, Bizen-ko-kabocha.
C. Pepo: Sômen, Pumpkin.
An appropriate medium for the pollen of C. moschata and C. maxima was prepared from 1.5 per cent agar-agar dissolved in a 50/100M solution of sucrose by boiling, its hydrogen-ion concentration being adjusted to pH 5.5. For C. Pepo, a medium of 6 per cent gelatine in 45/100M sucrose solution adjusted to pH 5.9 was the best.
The rate of germination tested in the afternoon was generally higher with the pollen of a flower-bud which was ready to open the next day than with that of an open flower. In the case of Shishigatani variety, the percentage of germination with pollen taken out from the flower-buds increased gradually with the lapse of time from morning till 9p.m. on the day before anthesis; it decreased slowly up to the blooming time early the next morning and then rapidly until 10a.m. of the same day. Pollen of Chirimen variety sustained its high germinative power during the forenoon after anthesis, but the reduction of its viability in the afternoon was prompt. From these features in C. maschata, the empirical rule that the pollination has to be done early in the morning seems reasonable. If the artificial pollination must be postponed to the afternoon, a satisfactory setting may be expected by pollination with the pollen of buds which are due to open the next day.
In the pollen of Hubbard, a high rate of germination was proved up to the evening after blooming. This agrees with BUSHNELL'S conclusion that successful pollination is possible at any time of the day.
