Abstract
It is suggested by various investigators that the self incompatibility is due to the action of a “special substance” which inhibits the germination of selfed pollen grains on the stigma or checks their tubegrowth later in the style.
Where is this substance produced? In order to answer the question, the author has tested the pollen-tube growth in the grafted style of Petunia violacea, and found out that the “special substance” is produced mainly in the ovary, and that it ascends to the upper parts of the pistil. The experimental results to this effect have been already reported.
What part of the ovary does secrete this substance? This is the question that demands the author to answer. So the scope of this paper will be confined to the discussion and the solution of the problem just mentioned. The germination and the tube-growth of the pollen of some self incompatible individuals were tested on various artificial media, each one of which contained different part of the ovary; the first kind of the media, which was the standard solution, contained nothing but 20% of cane sugar and a little amount of citric acid, the pH value of which was noted as 5.7-5.8; the other kind prepared by adding the tissue juice of the wall of the ovary to the solution of the first kind; the third was made by mixing the ovules to the first; and the last conntained the tissue juice of the placenta in the first medium. The results of these experiments indicate that the “special substance” exists little in the wall of the ovary and very abundantly in the placenta.
However, the inhibiting phenomenon was observed somewhat clearly also in the medium containing the ovules from the same individual. Thus, in order to see whether the special substance is secreted by the ovule or not, the author added, in his next experiment, washed ovules, to the standard solution. The inhibiting phenomenon was scarcely observed, or not at all in this case. Again, the author could not find any phenomena that may be called the escaping the. pollen tubes from the ovules which were added to the medium. In other word, the pollen tubes do not show nagative chemotropism toward the self ovules. From these results, it is evident that the “special substance” is by no means a product of the ovule.
In the third experiment, the pollen germination and the tubegrowth were tested on two series of media, one of which contained the tissue juice of the placenta of the same individual and the other the juice of the placenta of a different line. The inhibition occured only in the media containing the juice of the self placenta.
From the evidence observed in these experiments, it is proved that the “special substance” claimed to inhibit self fertilization, is produced in the placenta, at least, in the plant with which the author has worked.
