This work is a study on light-sensitivity of germination investigated by using the seeds of six species of Japanese-grown tobacco which are Yellow, Daruma, Oo-Daruma, Suifu, Hatano and Kokubu. In this study, the following subjects were investigated.
(1) How the degrees of light-sensitivity vary as
the time of presoaking* proceeds. *-the time during which petri dishes containing seeds are laid in a dark incubator as described below.
(2) How much light is required for obtaining the highest percentage of germination. (Light quantity will be expressed as meter-candle-second (MKS) Unit).
Seeds were disseminated over the surface of agar (1.5% aqueous solution) in petri dishes. Immediately after that, these petri dishes were wrapped in thick black papers, then they were put into a dark incubator. Each petri dish was taken out from the incubator after a definit time (a respective different time was given for each dish), stripped off . its black covering paper and was exposed to a definit quantity of light. (A 200-watt Toki bulb was used as a source of light.) Then it was again wrapped in the same black paper and put back to the incubator. On the 8th day after exposing each petri dish was opened and germination percentage was counted. Thus the follwing results were obtained.
1. Without regard to light quantity, light sensitivity showed a pronounced maximum when the times of presoaking reached certain hours, viz., 36hrs. for Yellow and Daruma, 48hrs. for Oo-Daruma and Suifu, and 72hrs. for Kokubu, and Hatano at 22°C each.
2. In case seeds were exposed to a small quantity of light, after each presoaking hours are passed, the light sensitivity is decreasing for sometime. This decrease cannot be seen in seeds which were exposed to a large quantity of light.
3. As to the light quantity required for the maximum percentage of germination of Hatano, Suifu, Daruma and Oo-Daruma seeds, the shorter the time of presoaking is, the more light quantity is required, in case the time of presoaking is less than 24hrs. However, when the time of presoaking exceeds 36hrs., the maximum percentages can be obtained by 2, 400, 000 M.K.S. and a greater quantity is not needed.
4. The seeds of “Yellow” are extraordinary sensitive to light. They proved that benefical effect of light was largely depending upon the length of presoaking hours rather than upon the light quantity.
The seeds of “Yellow” required only 100 M.K.S. for obtaining the maximum percentage of germination whenever the presoaking hours exceed 48hrs.. Besides, the author secured 79% germination after 48hrs. of presoaking by exposing them to light for a very few moment, (1, 500Lux, one-ninetieth second, 16.5 M.K.S.) whereas only very few of the seeds germinated in the darkness without such exposure.
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