did not save them. There never yet was armor without vulnerable point. Nature "arms and equips an organism to find its place and living in the world, and at the same time she arms and equips another to destroy it." Squirrels deftly open the hardest hickory nuts; larvæ penetrate the thickest-shelled almonds. Wallace describes how cleverly the black cockatoo of the Aru Islands breaks into the kanary nut, which is so hard that only a heavy hammer will crack it.
Every little helps, and the absence of the straw may save the camel. Therefore, if in addition to their hard coverings these fruits are also colored so as not to be easily seen, they have still another advantage. Mr. Bailey describes the pods of the sensitive pea as "protectively imitative," much resembling the leaves of the same plant when closed after irritation. Wallace thinks that the dry fruits of herbs "have no doubt often been prevented from acquiring bright colors by natural selection, in order to protect their seeds." And it seems logical that the same purpose may be served by the sober colors of the larger dry fruits.
Fuller describes a kind of figwort as a possible instance of a protectively colored flower. The blossoms are inconspicuous and purplish; the ripening ovary develops a dark purple tint, and somewhat resembles the fallen corolla; the buds, too, are as deeply colored as the opened blossoms, an unusual thing. Since this species is adapted to pollination by wasps, and avoided by other insects which have a respectful awe of their formidable sting, the miniature flowers and the fruits seem to be well protected by resembling the blossoms—an economical method to say the least, and so effective that the wasps themselves, sometimes deceived, were seen to alight on the buds and ovaries.
III. Warning Color.—In the forests of Nicaragua there is a brilliant red and blue frog, which is scornfully rejected by the birds who usually devour frogs and lizards greedily. All the other batrachians are protectively colored and feed only at night; but these little fellows hop boldly around with no thought of fear. A certain hermit crab is found always in shells which are covered with a (usually) bright-colored sponge or sea-anemone, both of which are avoided by the crab's enemies. In such cases striking color is correlated with obnoxious chemical qualities, and the enemies understand it.
It would be decidedly advantageous to plants which are not otherwise fitted to survive the attacks of herbivorous animals to accumulate substances offensive to them and then to advertise their disagreeable qualities as clearly as possible, either by peculiar form or color or odor; and what we are constantly learning of the sagacity of animals leaves little room for doubt that they would quickly recognize these species and shun them.