Culturing in dark would benefit the growth of callus and control of brown stain.

暗培养有利于愈伤组织生长，对控制褐化也有一定作用。

youdao

Hesper gasped with pain. She stared at the brown stain that splotched the front of her dress.

海茨帕因痛苦而目瞪口呆，瞅着她衣服前的污点。

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On one occasion, Miss Martha noticed a red and brown stain on his fingers and decided that he was a struggling artist.

有一次，玛莎小姐注意到这人的手指上有红棕色的彩渍，由此她断定这人是位尚不出名的艺术家。

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The result, after several days, was a sludgy brown stain at the bottom of the reaction vessel a stain that proved to contain amino acids.

ECONOMIST: Stanley Miller

"From outer space, all you can see at first is ice and a little brown stain, " said research fellow Michelle LaRue at the University of Minnesota's Polar Geospatial Center.

WSJ: Emperor Penguins Aplenty in Antarctica

The shavings were then immunostained bathed in a special reagent that would mark the presence of abnormal proteins with a bright, telltale red or brown stain on the surface of the tissue.

NEWYORKER: Offensive Play