Therefore, it is concluded that regulation of callus formation and differentiation of the calli by exogenous hormone is closely related to some endogenous factors and external condition.

因此，认为植物产生愈伤组织和再分化为植株不仅与外源激素有关，而且因植物材料和营养条件而异。

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And there has been one set of crises which are quite, to use the phrase, exogenous, external to the government which have befallen us.

BBC: Jack Straw MP. photo courtesy Jeff Overs

Unfortunately, the exogenous factors hitting the economy in the second quarter, both external and internal, are much worse than the first quarter, said Tony Volpon, head of emerging markets research at Nomura Securities in New York.

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