As our readers know, many flowers cannot fertilize themselves, but depend on insects to help them. In this way the pollen is often brought from other flowers than the ones fertilized, and this constitutes what is known as "cross fertilization by insect agency." In the January number of the American Agriculturist, Dr. Asa Gray has an article, written in the clear and happy manner he is noted for when he chooses to write to the popular mind, showing that Campanula, the well" known Bell flower of our gardens, is another addition to this miserably helpless class of plants.