Abstract: Prethrum cinerariifolium Trev. is the raw industrial material for extracting natural pyethrins,which exists in all parts of Pyrethrum plant,especially in ovaries in capitulum. The oil glands of vessels on ovary walls change from the formation and development to the transformation of secretion in the process of flower bud development ,flowering had seed maturation. The contents of pyrethrins markedly vary in different growing stages. It is divided into eight stages from the flower bud stage to maturation time of seeds,in order to understand the relationship between florets development stage and contents of pyrethrins in capitulum of Pyrethrum cinerariifolium.

Key words: Pyrethrum cinerariifolium, Flowering chracteristics, Pyrethrins, Oil gland, Dry matter, Suitable harvest time