Answer:
Directional selection
Step-by-step explanation:
Here, blue poppies which belonged to China were grown in drier climate of California. Plants who live in drier areas generally have thicker leaves to preserve water. Hence the blue poppies leaves also started to become thick and after several generations thick leaved plants had increased by 42%.
This phenomena would come under directional selection. In directional selection, one of the extreme phenotypes is preferred to adapt better to the environment. Here neither thin leaves were selected nor average leaves were selected, rather the selection preferred thick leaves which lies on other end of spectrum. Hence, this is an example of directional selection.