But the converse of this dependence is also largely true. Plants are beholden to animals for processes that in return make their own life possible. The latter minister to the former with unconscious service all the time, and with no more arrogant independence than do our domestics generally nowadays. The inconspicuous earthworm is the fieldhand of nature’s crops, who gets his own living by making theirs. Without this day and night laborer the soil for want of stirring had remained less capable of grass. Above ground it is the same story. Deprived of the ministrations of insects many kinds of plants would incontinently perish. By the solicited visits of bees and other hymenoptera—what generically may be classed by the layman as flutter-bys—is the plant’s propagation made possible. Peculiarly well named, indeed, are the hymenoptera, seeing that they are the great matrimonial go-betweens, carrying pollen from one individual to another and thus uniting what otherwise could not meet. Spectacular as this widespread commerce is, it forms but portion of the daily drama in which animals and plants alike take part. From forthright bargainings of honey for help, we pass to less direct but no less effective alliance where plants are beholden to animals for life by the killing of their enemies or the weeding-out of their competitors, and from this to generic furtherance where the interdependence becomes broadcast. In the matter of metabolism the advantage is not all upon one side. In the katabolic process of that which each discards are the two classes of life mutually complimentary,—the waste of the one being the want of the other,—carbonic acid gas being given off by the animal, oxygen by the plant. In biologic economy it is daily more demonstrable that both are necessary constituents to an advancing whole, and that each pays for what it gets by what it gives in return.