Natural and artificial selection — practice question

The monkey flower, Mimulus guttatus, is pollinated by bumblebees rather than by self-pollination. Because bumblebee numbers are declining in many parts of the world, an experiment was done in Kansas to see how these plants are affected when pollinators are lost. - 1600 Mimulus plants were grown in a field. - 1600 Mimulus plants were grown in a glasshouse that bumblebees were unable to enter. For several generations, seeds were collected and sown again and again at both sites. At the start, the glasshouse plants produced few seeds, but after five generations they were able to self-pollinate and the number of seeds produced was almost the same as that of the field plants. By the end of five generations, the flowers of the glasshouse plants were significantly smaller than those of the field plants.