It occurs in a very long, metaphoric passage. In the same article, Martin actually calls New York City other things, such as the "frontier city," a "museum," and "a very tall horse." I've checked Martin's many other works without finding another "big apple."
Here are selections from The Wayfarer in New York (NY: Macmillan, 1909):
Pp. xiv-xv: But at home Kansas is apt to see in New York a greedy city, wrapped up in itself, incredulous of western wisdom, inhospitable to "broad American ideas," perched on the shore of the Atlantic Ocean and careless of the great land behind it except as a vast productive area from which it draws endless wealth. New York is merely one of the fruits of that great tree whose roots go down in the Mississippi Valley, and whose branches spread from one ocean to the other, but the tree has no great degree of affection for its fruit. It inclines to think that the big apple gets a disproportionate share of the national sap. It is disturbed by the enormous drawing power of a metropolis which constantly attracts to itself wealth and its possessors from all the lesser centers of the land.
Pg. xi (first line): NEW YORK is a frontier city situated about halfway between San Francisco and London.
Pg. xxi: An important fraction of the annual immigration that lands at Ellis Island clings to New York and gets no farther. Therein lies her title to be called a frontier city...
Pg. xxi: Ethnologically, as every one knows, New York is a museum.
Pg. xxii: To ride a tall horse does not make a man great, but it may make him look great and even feel great. New York is a very tall horse, and many who ride her look bigger and feel bigger for that exploit.
This citation was recorded in the 1980s by a librarian in the New-York Historical Society. It would be a large stretch to say that Edward Martin called New York City "the Big Apple" even in this essay, since so many other metaphors are used. Big Apple" doesn't show up in Martin's work again. Our next "Big Apple" is from John J. Fitz Gerald in the 1920s, and he admits hearing the term first in New Orleans.
For all of these reasons, the Historical Dictionary of American Slang and other scholars record, but discount, this use.
New York City • The Big Apple • 1970s-present: False Etymologies • Monday, July 12, 2004 • Permalink