See downloadable PDF file, above.
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Professor Jack Salzman has answered this question definitively with a yes. Dreiser did plagiarize — contrary to the assessment of Dreiser biographer W. A. Swanberg — from George Ade (1866–1944), an Indiana born newspaper columnist, humorist, novelist, short story writer, and playwright, in a passage in the opening chapter of Sister Carrie.
See Jack Salzman, “Dreiser and Ade: A Note on the Text of Sister Carrie,” American Literature, vol. 40, no. 4 (January 1969), pp. 544-548 — posted here as a downloaable PDF file.
Thanks to Professor Salzman for permission to post this article.
— Roger W. Smith
See also:
“George Ade Absolves Dreiser”
https://dreiseronlinecom.wordpress.com/2016/02/23/george-ade-absolves-dreiser/