The Argentina 1935-51 definitives issue combines beautiful designs, interesting color and plate varieties, and an expansive postal history punctuated by World War II. One of the most strikingly beautiful of these stamps is the 5 Pesos value. I show examples here from the first printings (5P1E), all on paper with the first watermark. The cover pictured below is an early usage to the Caribbean Island of Trinidad. It was mailed to a passenger aboard a ship. The 35-8-? marking is likely the passenger's berthing and was likely penciled in by someone on board. The stamps were postmarked "AGENCIA 5/13-B.AIRES."

A detail of the high values is shown below.

The cover pictured below was mailed to New York City in 1944. It bears typical U.S. censorship markings typical of the late World War II period: tape with ink identification number.

This cover bears a single 5P1E, two singles of the 2P1E, and a single of the 5c1E, postmarked BUENOS AIRES C. {CENTRAL} 2."

Recommendations for further browsing:

I have a page with many covers of this printing as well as the later printings of the 5 Pesos Iguazu Falls.

The continental grain correspondence page contains several 5 Pesos Iguazu Falls covers.

The Argentina 1935-51 issue pages from the 5 pesos types page there is additional information about each of the printings.

Also, an early article dedicated to a lower value in the series, Article 5: Issues of the 20c "Large Cow" (20cLC) Value.