Studies in Vernalisation: XI. The Effects of Date of Sowing and of Excising the Embryo upon the Responses of Petkus Winter Rye to Different Periods of Vernalisation Treatment

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Abstract
When embryos of winter rye, Se-cale cereale var. Petkus Winter, excised from the grain, are vernalized on a sucrose medium, the rate of the process at first lags behind that in whole grain, after which it is the same in both. During this "lag" period a substance requisite for vernalization, normally transferred from the endosperm or aleurone layer, may be synthesized by the embryo. The synthesis or accumulation of this substance in the excised embryo and its transference from the endosperm in whole grains require low temp. It cannot be replaced by heteroauxin, dried yeast or ground rye endosperm. A delay in the inception of vernalization also appears when whole grain is planted late (May 17). A sowing-date expt. showed that this delay is different in origin and due to factors operating after planting. The progress of vernalization in intact grain may be represented by a sigmoid curve, conforming with that of an autocatalytic reaction. The actual curves deduced from flowering behavior vary in form with the sowing date, and with conditions of culture. Thus, pot cultures are consistently earlier than field cultures. Early sowing (April 5th) gives an apparently linear relationship; late sowing retards partially vernalized plants while accelerating those fully vernalized. These modifications of the fundamental curve are examined in relationship to air and soil temp. and varying day-length, and the major features may be accounted for by the action of these factors.