But the most significant botanical contrast and distinction is found in the union of the style and stamens in one organ, called the column (Fig. 2), the stigma and the pollen being thus disposed upon a single common stalk. The contrast to the ordinary flower will be readily appreciated by comparison of the accompanying diagrams (Fig. 1). When, therefore, we find a blossom with the anthers or pollen receptacle united to a stalk upon which the stigma is also placed, we have an orchid. The order is further remarkable, as Darwin first demonstrated in his wonderful volume "The Fertilization of Orchids," in that the entire group, with very few exceptions, are absolutely dependent upon insects for their perpetuation through seed. They possess no possible resource for self-fertilization in the neglect of these insect sponsors. [Illustration: Fig. 2 a. Anther. s. Stigma.] Many of our common wild flowers, as perfectly and effectually planned for cross-fertilization as the orchids, _do_ retain the reserve power of final _self_-fertilization if unfertilized by foreign pollen. But the orchid has lost such power, and in the progress of evolution has gradually adapted itself to the insect, often to a particular species of insect, its sole sponsor, which natural selection has again gradually modified in relation to the flower. The above work by Darwin was mostly concerned with foreign species, generally under artificial cultivation, and so startling were the disclosures concerning these hitherto sphinx-like floral beings that a most extensive bibliography soon attested the widespread inspiration and interest awakened by its pages. But it is by no means necessary to visit the tropics or the conservatory for examples of these wonders. Our own Asa Gray, one of Darwin's instant proselytes, was prompt to demonstrate that the commonest of our native American species might afford revelations quite as astonishing as those exotic species which Darwin had described. [Illustration: Fig. 3] During a period of many years the writer has devoted much study to our native species of orchids from this evolutionary stand-point of their cross-fertilization tendencies. Of the following examples, selected from his list, some are elaborations of previous descriptions of Gray and others, though pictorially and descriptively the result of direct original study from nature; others are from actual observation of the insects at work on the flowers; and others still, original demonstrations based upon analogy and the obvious intention of the floral construction, the action of the insect--its head or tongue--having been artificially imitated by pins, bristles, or other probe-like bodies.