YUCCA MOTH AND YUCCA POLLINATION. 101 
The most casual observer of nature must have appreci- 
ated, years ago, the fact that flowers are very important to 
insects, furnishing the essentials of life to those of several 
orders and especially to the Hymenoptera (Bees, Wasps, 
ete.) and Lepidoptera (Butterflies and Moths) in the form 
either of pollen or nectar. But that insects could be of 
any especial benefit to plants has only come to be acknowl- 
edged and fully appreciated of late years. Toward the 
close of the last century Christian Konrad Sprengel pub- 
lished an important work — Das Entdeckte Geheimniss der 
Natur — in which he muintained that the color, form, odor, 
secretions, and the general structure of flowers had refer- 
ence to insects which are essential as pollinizers. The 
importance of insects as agents in cross-fertilization was 
scarcely appreciated, however, until the late Charles Dar- 
win published the results of his researches on Primula, 
Linum, Lythrum, etc., and his elaborate work on the fer- 
tilization 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 Spe- 
cies’ to the general study of biology. Hooker, Bennett, 
Axell, Delpino, Hildebrand, Hermann Miiller, and others 
abroad, and Dr. Gray and Mr. William Trelease in this 
country, have followed up this subject; and no one can 
familiarize himself with the results of their studies with- 
out 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 usu- 
ally 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 excep- 
