Sentence:  After they are shot up thirty feet in length, they spread a very large top, having no bough nor twig in the trunk or the <WSD>stem</WSD>. 
Meaning of the word marked with <WSD> tags:  The above-ground stalk ("technically" axis) of a vascular plant, and certain anatomically similar, below-ground organs such as rhizomes, bulbs, tubers, and corms.