0 in plants with flowers, a hard layer that covers and protects the surface of a seed -- 外种皮（覆盖和保护种子表面的硬皮）
This testa probably reduced the rate of water loss and protected the embryo from physical injury.
In four instances, the testa was removed from one end of the seed and the fleshy cotyledons eaten from the centre.
In both species, seeds lacking testae began to soften about day 8, were often attacked by fungus, and had rotted completely by day 10.
In this work, emphasis is placed on the existence of seed mutants having major alterations in characteristics of the testa and hormonal response.
The testa epidermis is peculiar in that the outer walls of dry seeds are invaginated, while they bulge outwards in wetted seeds.
Seeds were considered germinated when the embryo had just ruptured the testa.
It is, therefore, tempting to ascribe more rapid completion of germination to an ethyleneinsensitive testa developing in an ethylene-insensitive environment.
Progress of testa rupture is facilitated by channels underlying the ridges.
