Answer:
In the excerpt above, the phrase "stiff collars wilted by nine in the morning" suggests that despite the heat, men still dressed up.
Step-by-step explanation:
The excerpt "Somehow, it was hotter then: a black dog suffered on a summer’s day; bony mules hitched to Hoover carts flicked flies in the sweltering shade of the live oaks on the square. Men’s stiff collars wilted by nine in the morning. " describes the place as having an unbearable hit but still the man preserved they regular dressing code, this is stated in the line "stiff collars wilted by nine in the morning" which means that because of the hit and the sweat the shirts of the man do not look as tidy and formal as they should by that time of the day.