Abstract
1. The author investigated the pollen tube growth in interspecific pollinations of the genus Cucurbita, with the intention of confirming the relations between the pollen tube growth and cross-compatibility.
2. The size of floral parts in female flowers varies according to species and varieties. For the comparison of the pollen tube growth it was measured respectively (Table 1).
3. The time for pollen tubes to make its way from stigmas to ovaries is as follows: In C. pepo var. Delicata it takes three hours to reach the ovaries, while in C. moschata vars. Futtsu Kurokawa and Aizu Gokuwase it requires four hours and in C. maxima var. Delicious five hours.
4. As seen from the degree of the pollen tube growth, the Cucurbita crosses can be classified into the following three combinations:
(a) The first case of combinations where pollen tubes are able to grow deeply into ovaries, reaching the end of main conducting tissues; C. maxima×C. moschata (Fig. 3), C. moschata×C. maxima (Fig. 6), C. maxima×C. pepo (Fig. 4).
(b) The second case of combinations where the pollen tube growth is delayed within the ovaries; C. moschata×C. pepo (Fig. 7).
(c) The third case of combinations where the pollen tube growth is inhibited at the upper regions of ovaries; C. pepo×C. maxima (Fig. 9), C. pepo×C. moschata (Figs. 10, 11).
5. From the results mentioned above and the percentages of fruit set obtained by the present author and other investigators, it may be said that crossings between C. maxima and C. moschata are of imperfect compatibility (Tables 2, 3).
6. The proper time for measuring the pollen tube growth may be 27-30 hours after the pollinations.
7. The peculiarity of C. pepo as staminate as well as pistillate parents was discussed.
