| 词汇 | testa |
| 释义 | testa noun[ C ] biology specializeduk /ˈtes.tə/ us /ˈtes.tə/pluraltestae 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） Parts of plants axil bark bilobed blade caning cascara sagrada corolla endodermis floret inflorescence knot pistil rooty rosella seed coat seed pod sessile sting taproot vein Examples of testatesta 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. The molecular data presented here are consistent with the anatomical and biochemical differences between the wild-type and the mutant testae. The completion of germination was defined as the radicle visibly protruding from the testa. A slow rate of ethylene production was found in these seeds, the testa being the source. The mutant 20-dpa testa did not stain blue (instead it stained purple), and hypodermal cells were not reticulated (data not shown). I suggested a mechanical function of the testa. Small bites had been taken from another seed although there was no evidence that the testa had first been removed. From a small area of the dry seed surface the testa was removed and 5 mg of flour was scratched from the cotyledons. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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