The main stem will extend to around 12 ft, if left to develop naturally.

如果让其自然生长，主干会延伸到12英尺左右。

《柯林斯英汉双解大词典》

A tree is a tall, woody plant that usually has one main stem, or trunk.

树是一种高大的木本植物，通常有一根主干，或树干。

youdao

Finalleaf number on main stem could be a reliable measure for wheat vernalization response.

主茎总叶数的变化是量测小麦春化反应性的一个可靠指标。

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The research suggests that to grow, they have to be able to export the hormone into the main stem.

VOA: special.2009.10.13

The new research shows that the buds on the side cannot export their auxin into the main stem because it is too full.

VOA: special.2009.10.13

Cut the main stem about twelve to fifteen centimeters below the head.

VOA: special.2010.03.09

The die-off was least severe in the southern bay, where there was a 7 percent overall decrease and where new beds were found in the main stem of the James River.

WSJ: Chesapeake Bay grasses decline again

Over the years, I gradually worked my way downstream from the West Branch to the big riffles and eddies of the Main Stem, where wild rainbow trout, more tolerant of warmer temperatures, reign supreme for the 35 miles between Hancock and Callicoon.

FORBES: Catskills Fly Fishing Book

That pluripotent ability, and the fact that stem cells self-renew, is the main attraction of stem cells from human embryos.

FORBES: Magazine Article