Developmental Anatomy and Relative Permeability of Barley Seed Coats

Abstract

1. The developmental anatomy and morphology of the barley caryopsis has been discussed and illustrated. 2. The selective semipermeable envelope has been identified as the persistent crushed and cutinized inner integument together with the suberized, resistant tissue of the chalaza. 3. The inner integument has a thin inner cutin membrane and a much thicker outer cutin layer of variable thickness. The thickest portion is over the apex of the kernel near its attachment to the chalaza. It is also very thick over the flanks of the endosperm in the groove, is thicker laterally than anteriorly, and it is thicker apically than proximally. It is very thin over the embryo, its thinnest portion being the area immediately across the grouped cells at the micropyle. The thickness of these membranes was found to vary with the variety studied. 4. Relative permeability of the seed coats has been determined in two ways, by the rate of absorption from aqueous solution, and by the electrical conductivity of seed coat membranes in aqueous solutions of electrolytes. 5. With the use of these two differing methods it has been determined that: varieties exhibit wide differences in degree of permeability (the hulled varieties as a group being less permeable than the hull-less varieties); a wet environment during maturation induces a decreased resistance to permeation; and harvesting prematurely also induces a slightly decreased resistance to permeation. 6. The differences found in relative permeability could not be correlated definitely with any one existent variation in the anatomical structure of the semipermeable seed coat envelopes of the caryopsis. With some varieties, however, the heavier layer of cutin on the integument and the heavier deposits of the fat substance in the integument cells seem to be correlated with an increased resistance to permeation. 7. The hull-less varieties investigated, as a group, were found more permeable than the hulled varieties but this difference was independent of the presence of the hulls.