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THE POPULAR SCIENCE MONTHLY 



agents in cross-fertilization was scarcely appreciated, however, 

 until the late Charles Darwin published the results of his re- 

 searches 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 al- 

 most as great an impulse as did his immortal Origin of Species 

 to the general study of biology. Hooker, Bennett, Axell, Del- 



Fig. 1. Flower of Yucca aloifolia, showing stouter pistil and shorter style as compared 



with filamentosa. 



pino, Hildebrand, Hermann Muller, 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 popu- 

 lar names of "four o'clock" and " John-go-to-bed-at-noon" suf- 

 ficiently 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 



