This change of color gives rise to another interesting peculiarity. If Arnebia be examined by daylight, and again in the dim twilight, the observer is struck by a remarkable circumstance. In broad daylight, the golden spotted flowers at once arrest the eye, while their paler companions are hardly observed. The inflorescence owes by far the greater part of its display to the younger flowers. In the dusk this is entirely reversed; the conspicuousness of the inflorescence now depends on the paler flowers, and the others are so obscured that a second glance is needed before they can be discerned. The relative brilliancy of the two sets of flowers can also be tested by gradually retiring from the plant, keeping the eyes still fixed on the blossoms. At dusk the young flowers are lost sight of much sooner than the others; by day the older ones first disappear in the distance. This peculiar transformation imparts to the inflorescence of Arnebia a faint similitude of the pillar of cloud by day and of fire by night--that celestial manifestation of sacred story so closely associated with the native region of this desert flower. Here, then, we have one of those phenomena which for the naturalist possess all the fascination of a mystery. What can be the explanation of this remarkable change of color, and what advantage does the flower derive from the sudden disappearance of its spots and the blanching of its petals? With the reader’s permission, we shall now proceed to show why nature has bestowed on Arnebia what she has denied to the leopard--the power of changing its spots. Before we can say why any flower should change its color, we must first know why a flower is colored at all, and why all flowers are not colored alike. Almost all the peculiarities of flowers can be explained as having reference to the visits of insects. The honey is secreted as an inducement, while the secret and brilliant colors serve to attract the attention of the honey-gatherers. The researches of the late Charles Darwin demonstrated the importance of cross-fertilization in the vegetable kingdom. Very many flowers are quite sterile with their own pollen; in other cases, although the flower has the capacity of self-fertilization, the resulting seeds are of very inferior quality compared with those obtained as a result of cross-fertilization. As carriers of pollen, then, insects perform an essential service to plants, and it is in order to secure their services that flowers are brightly colored.