Page:Popular Science Monthly Volume 42.djvu/92

 82 these, a few individuals of rare species, themselves defenseless and palatable, differing widely from the type of the genera to which they belong, and so closely resembling the others as to be readily mistaken for them even by experienced collectors. Since its discovery, numerous examples of this so-called "mimicry" have been brought to light in many classes of animals, its conditions being always the same. A rare, helpless species is protected from attack by similarity, in external appearance only, to a common, easily recognizable, well-defended one.

There are strong resemblances between widely separated genera of plants. The submerged parts of water-crowfoots are much like those of water-marigolds. "It is almost impossible to distinguish between" the euphorbias of Africa and the cacti of South America, when not in blossom; mare's-tail looks like an equisetum—one is a flowering, the other a flowerless plant; the false goat's-beard closely resembles the true; dalibarda "in aspect and foliage resembles a stemless violet." Observation may find proof of some advantage gained to the feebler plant by the likeness in the last two cases, inasmuch as the plants occupy the same localities, and in each case one of the species is much more limited in distribution than the other. But none of the others are examples of true mimicry, because the similar plants do not inhabit the same regions, and it is hardly supposable that any benefit accrues from the likeness. Similarity of conditions may have much to do with it in some instances, but a deeper cause, and one of a kind which we can not yet conceive, must be sought in explanation of the extraordinary results sometimes reached.

Nevertheless, there is true mimicry in plants.

The only South African balsam is strikingly like an orchid which grows in the same locality and is visited by the same insects! Surely a clear case of plagiarism.

The "cow-wheat" is parasitic upon the roots of wheat, whose seed its own so exactly resembles that the two can only be distinguished by careful botanical examination. So the husbandman who himself sows tares among the wheat, one day wakes to say, "An enemy hath done this."

Sir John Lubbock thinks that the harmless dead-nettle may be protected from grazing cattle by its great likeness to the stinging nettle—a member of a widely different order.

In 1833 Robert Brown conjectured that the remarkable insect-like forms of the flowers of the genus Ophrys (bee orchid, etc.) "are intended to deter, not to attract insects." But Darwin has shown that some of the species are self-sterile, and all of them are constructed as though insects had played an important part in the shaping of the floral organs. The native home of the genus is the Mediterranean region, where all kinds of methods of defense