The mature achene is composed of a hard and relatively thick pericarp, a thin testa , an endosperm consisting of one cell layer, and a small embryo.
In those studies, the fast-drying condition was normally referred to as the dehydration of seed tissues under a laminar flow cabinet or with silica gel, while slow-drying was the drying of seed tissues with testa or in closed containers.
A reddish tinge signifies penetrance of the dye through the testa into the endosperm and embryo.
While the subaleurone cells were intensively labelled, no label was seen in the outer layers of the grain, i.e. in the testa , pericarp and husk.
Wheat grains consist of the seed coat, or testa , which surrounds the endosperm and embryo.
The single-seeded fruit known as a caryopsis consists of the pericarp and testa surrounding the endosperm and the embedded embryo.
In plants, ethanol is produced in seeds with an oxygen-impermeable testa , root tips, and the deep tissues of ripening fruit where there is a high demand for oxygen.
The seeds' hard testa is an effective protective structure allowing them to survive fire, and being passed through the guts of large animals which aid dispersal.
Except at the crease, the endosperm is encased in the testa with its inner and outer cuticular layers and so, from this stage onwards, only the symplastic pathway through the chalazal cells is available.
Sufficient moisture must be present to penetrate the testa or seed coat, but not so much that the seed rots or that the oxygen level in the soil is reduced.