Physiological Researches on the Fertility in Petunia violacea VII

On the Cause of the so-called “End-season Fertility”

Abstract

It was observed and studied by several investigators, such as DARWIN, EAST, PARK and STOUT, that some self-sterile plants often become self fertile toward the close of their flowering season. STOUT called such a phenomenon the “end-season fertility.”
The author has been at work since 1927 to make the cause of this phenomenon clear in Petunia. The materials used in his experiments consisted of two kinds of individuals, namely, the “old” and the “vigorous” ones in each line. The “old” individuals were cultured in pots for two succeeding years and their growth were very weak, while the “vigorous” ones were obtained by cutting method from some branches of the former and their growth were very vigorous.
The results of the experiments were as follows:
1. The flowers of each material were intra-self pollinated. In the self-incompatible lines the “old” individuals gave better results than the “vigorous” ones. These facts show us that the “end -season fertility” is caused by some internal conditions rather than the external ones, for each pair of pollinations was done at the same time.
2. The phenomenon of perthenogenesis was not observed in each individual during these years. Therefore the “end-season fertility” is by no means caused by such a phenomenon as parthenogenesis, at least in Petunia.
3. The pollen grains of one flower were applied to the stigmas of different individuals of the same vegetative line. The results obtained in these cases were nearly the same with those obtained with the intra-self From these facts we may infer that the cause of the “end-season fertility” may be said to lie in some changes of the character of the pistil rather than that of the pollen.
4. But, on the contrary, when the flowers were pollinated with the pollen of the other line, each capusule of the “old” individuals contained fewer seeds than those of the “vigorous” ones. Therefore the results of this experiment will show that the “endseason fertility” is not due to the increase in the number nor the fertility of the ovule.
5. The germination of the pollen was tested with two kinds of sugar solutions; into the one of them was added the stigmasecretion from the “old” individual and into the other that from the “vigorous” one of the same vegetative line. In the selfincompatible line the pollen germinated more easily in the former solution than in the latter.
6. The growth of the pollen tubes in two kinds of sugar solutions was observed. Into one of the media the tissue juice from the style of the “old” individual was added, but into the other that of the “vigorous” one of the same vegetative line was substituted. In the self-incompatible line the tubes grew more rapidly in the former medium than in the latter.
7. But in the self-compatible line, it was not observed that the fertility of the pistil with the pollen of the same flower or that of the different flower of the same vegetative line increased at the end of their flowering season.
And moreover nearly same results were observed in the germination of the pollen or the growth of the pollen tube regardless of the stigma secretion or the styler juice, both of which were added to the culture media taking either from the “old” or the “vigorous” individual, provided they are of the same vegetative line.
The author has reported in his previous papers that in his Petunia of self incompatible lines the stigma-secretion and the tissue-juice of the style seem to contain a snbstance or substances unfavourable for the germination of the pollen or the growth of the pollen tube of the same flower or of the same vegetative line.