"Because innovation is subject to historical changes - many of which are themselves the result of influential innovations in the transmission of information - the four quadrants display distinct shapes at different historical periods" (p 226).
Essentially, what Johnson is saying is that to reach the fourth quadrant innovations come from the building of ideas on innovations that were already presented as the stage for further development. This clearly relates to platforms and ideas that were previously presented that allowed innovations to develop over time. This suggests that innovations reach the fourth quadrant from an environment in which ideas are constantly developing.
This idea also correlates to evolution and things I have learned in my Evolution course. Essentially, evolution is change over time, but over time new ideas or traits come about from things presented prior. This relates back to coral reefs in which Johnson talked extensively about again in this last chapter. Over an historical time period, new developments came about from observing the coral reefs.