agents in cross-fertilization was scarcely appreciated, however, until the late Charles Darwin published the results of his researches on Primula, Linum, Lythrum, etc., and his elaborate work on the fertilization of orchids. The publication of these works gave to flowers a new significance and to their study almost as great an impulse as did his immortal Origin of Species to the general study of biology. Hooker, Bennett, Axell, Delpino,
Fig. 1.—Flower of Yucca aloifolia, showing stouter pistil and shorter style as compared with filamentosa.
Hildebrand, Hermann Müller, and others abroad, and Dr. Gray and Prof. William Trelease in this country, have followed up this subject; and no one can familiarize himself with the results of their studies without a keen sense—if not a conviction—that in the vast number of cases Sprengel's early statement holds strictly true. By these deeper insights into the significances of the floral world, and their harmonies with the insect world, we learn to understand why night-blooming flowers are usually white, even where their day-blooming allies are brightly colored, as in the case of Lychnis vespertina and L. diurna; or why the calyx, which is usually hidden and green, becomes bright when exposed, as in the berberry and larkspur. Many flowers are known to close or "sleep," and while most of them follow the animal world in taking this rest at night, yet there are marked exceptions. The dandelion goes to rest at 5 p. m. and wakes at 7 a. m., while the popular names of "four o'clock" and "John-go-to-bed-at-noon" sufficiently indicate the sleeping hours of Mirabilis and Tragopogon. Sir John Lubbock tritely asks, "What is the meaning of sleep in flowers, if it is not in reference to insects?" The closing during those hours when the particular insects needed for pollination
