Studies on the Germination of Cereals

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Abstract
The uptake of water by imbibition, vacuolation, and growth of the embryo, has been determined when wheat grains were placed under germination conditions before maturation was completed; and the effect of the covering layers has been investigated in a red and a white variety at three stages during ripening. The water lost during ripening was replace by imbibition without causing the embryo to expand sufficiently to rupture the covering layers. The cells of the coleorhiza and epiblast absorbed water by vacuolation as soon as they were imbibed; but afurther period elapsed before the scutellum became imbibed and water uptake was associated with an increase in embryo dry weight. In both varieties, uptake opf water by the imbibed embryo was prevented by the inner layer of the pericarp and the tesa in unripe grains, and by the epidermal layer of the pericarp during the early staes of ripening. But after the final stage of rapid desiccation the covering layers of the white grains were ruptured when the embryo absorbed water by vacuolation; whereas the covering layers of the red grains remained intact and the uptake of water was delayed until a sufficient period had elapsed for nutrients from the endosperm to be available for growth ofr the embryo. The varietal difference in germinationj is therefore attributed to the greater strength of the covering layers of the red grains, which are not disrupted during ripening, and prevent expansion of the embryo until the water absorbing capacity has been increased by the transfer of reserves from the endosperm.

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