It would be impossible to give any adequate account of the subject of insect-pollination in general, as it is an immense subject with an ever-increasing literature. Every kind of flower has its own particular way of solving the problem, so that the subject will never be completed until all flowers have been questioned and their answers obtained. Any account, however brief, should not omit mention of the orchids, which in the matter of insect-pollination have reached the highest degree of organization. So detailed are their adaptations that each kind of flower is adapted to a particular kind of insect. The accounts given of the various ways in which orchids attract insects and secure pollination really surpass belief, until one has actually observed some of the plants and their insects at work. Any greenhouse furnishes abundant examples of orchids, and our illustration represents one of the most common of our native orchids, the ordinary yellow Lady-slipper. In most orchid flowers there is a long tubular spur, at the bottom of which the nectar is found, which is to be reached by long probosces, such as can be found only in moths and butterflies. In Lady-slippers, however, there is a different arrangement. The flowers have a conspicuous pouch in which the nectar is secreted, and a flap overhangs the opening of the pouch. Behind the flap are the two pollen masses, between which is the stigmatic surface. A bee crowds itself away into the pouch and becomes imprisoned, and may frequently be found buzzing about uneasily. The nectar is in the bottom of the pouch, and after feeding the bee moves toward the opening overhung by the flap, and rubs itself against the stigma and then against the anthers, receiving the pollen on its back. A visit to another flower will result in rubbing some of the pollen upon the stigma, and in receiving more pollen for another flower.