Abstract
(1) The present author has succeeded to induce artificially the disturbance of the meiotic division of the pollen mother cells of a pure strain of the balsam plant, by exposing the plant materials to high temperature. The meiotic division of the pollen mother cells of this strain, observed during the summer time at Taihoku, is so unstable that it took place quite normally in some days and behaved very abnormally in other days.
(2) The plant materials were exposed to different, constant temperatures by keeping them in a thermostat for 5 hours. Immediately after the treatment, the mode of meiosis of the pollen mother cells was examined.
(3) The meiosis is practically or quite normal at the temperature below 28°C., while it is irregular at above 30°C. (Table 1). The irregularities become extreem with the rise of temperature, not only in the number of affected pollen mother cells, but also in the degree of irregularity observed in each cell.
(4) The principal types of the abnormality observed in these cases are as follow:-
(a) At the first meiosis: Lagging of a few bivalent chromosomes (Fig. 6); too early (Fig. 1), or too late disjunction of several gemini (Fig. 2); appearance of univalent chromosomes before the metaphase (Fig. 4.7); scattering over of all chromosomes throughout the spindle (Fig. 5), or throughout the cytoplasm (Fig. 7, 17); random disjunction (Fig. 16); etc.
(b) At the second meiosis: Too early splitting (Fig. 7); scattering over of most of the chromosomes throughout the cytoplasm (Fig. 8); wandering of a few chromosomes in the cytoplasm (Fig. 9); formation of a giant equatorial plate consisting of univalent chromosomes (Fig. 10, 11); random splitting (Fig. 11, 12, 13); union of two equatorial plates (Fig. 14); random gathering of the chromosomes in the late anaphase (Fig. 15); etc.
(5) In summarising the results of the experiment, the author has concluded that the unstability of the meoisis of the pollen mother cells of the balsam plant in question must be due to the effect of air temperature, because, this unstability is usually observed at Taihoku during the summer time when the air temperature attains frequently above 30°C. At this temperature, the meiosis of the pollen mother cells of this plant reaches to the critical point resulting abnormality.
