Observing the development of flowers into fruit
Collect specimens of flowers in dissimilar stages of maturity from newly opened buds to specimens in which the petals have fallen. Cut every ovary open and note the changes that take place during seed development.
Look over a quart of freshly picked peas or string beans and pick out the pods that are not fully filled. Open these and compare them with completely filled specimens. The abortive seeds are the remains of ovules that were not fertilized by pollen..