Green’s Dictionary of Slang

main stem n.

[SE main stem, the central trunk]

1. [late 19C–1930s] (US) a person of importance, the boss.

2. [late 19C+] (also big stem) the main street of a town.

3. [20C+] (US black) attrib. use of sense 2, stylish, sophisticated.

4. [1920s–30s] (US tramp) the most important street of a town in the context of tramp society and standards.

5. [1920s–50s] Broadway, New York City.

6. attrib. use of sense 5.

In phrases

buzz the main stem (v.) (also mooch the main stem, work the main stem)

[1920s] to beg along a town’s main street.

on the stem

[20C+] (US tramp) walking the main street of a town, begging for subsistence.