PHOENIX, July 25 (Reuters) - Arizona's saguaro cacti, a symbol of the U.S. West, are leaning, losing arms and in some cases falling over during the state's record streak of extreme heat, a scientist said on Tuesday. Summer monsoon rains the cacti rely on have failed to arrive, testing the desert giants' ability to survive in the wild as well as in cities after temperatures above 110 degrees Fahrenheit (43 Celsius) for 25 days in Phoenix, said Tania Hernandez.