Darwins explanation for evolution was dependent on which specific concept

During an experiment, readings for blood pressure in a persons body were found to be constant . however , when he measured by a different blood pressure cuff , the readings differed by 15 points for each reading. this difference indicates that the results are

The structure that houses the cells genetic information.

Up to what percentage of the world's flora consisted of cycads during the triassic period? 100% 75% 50% 20%