海带的生长发育过程中,共划分六个时期:即幼龄期、小海带期、薄嫩期、厚成期、成熟期和衰老期。叶片出现平直部,是薄嫩期的一个主要表现形态。平直部形成的早晚和大小,直接关系到经济效益的高低,是海带质量优劣的主要指标。在国家颁布的等级标准中,明确规定:平直部70厘米以上为一级品,50厘米以上为二级品,40厘米以上为三级品。同时规定:平直部不足15厘米长度的海带即作为等外品。 Kelp growth and development process, divided into a total of six periods: young age, small Kelp period, thin tender period, thick mature, mature and senescent. The emergence of flat leaves, thin is a major manifestation of tender period. The formation of flatness sooner or later and the size, is directly related to the level of economic benefits, is the main indicator of kelp quality. In the country promulgated by the level of standards, clearly states: 70 centimeters straight for the first grade, more than 50 cm for the second grade, more than 40 cm for the third grade. At the same time provides: straight part of less than 15 cm length of the kelp that is as the other goods.