This process of reproduction, by simple division, was early supplemented by another process of reproduction in which two living cells first fused or combined and then divided to form two or more daughter-cells. This form of reproduction seems to have added stimulus or vitality to the organisms. The supposed reason for this is that the isolated cell was inclined to weaken or lose its chemical balance or tone. The exact nature of this deterioration is not very clearly understood, but in a higher form of life it is well illustrated by the tendency of certain plants to "run out" when grown continually in the same soil, or of animals to become weakened when inbred. At least, all scientists concede that with the process of fusion or the combining of two cells there is added a stimulating and invigorating force which enables life to combat more successfully the unfavorable elements of its environment, and to change or evolve into higher forms. [Sidenote: Sexual reproduction in plants] [Sidenote: Fertilization of orchids] Throughout the range of plant and animal life this process of cell union, or sexual reproduction, has grown and become elaborated into most varied and wonderful forms. Large volumes could be written describing the many wonderful adaptations of plant and animal life, the purpose of which is to secure sexual reproduction. All those who have studied botany are familiar with the many ways in which the seeds of plants are fertilized by pollen. For instance, certain species of orchids have a receptacle in the blossom, shaped like a teapot, which is filled with a fluid resembling water. This little teapot has an entrance and an exit. Near the entrance is sweet-scented nectar which attracts the bee. As the bee passes through this gateway he is tripped up on a little trap-door arrangement and precipitated into the fluid. His wings having become wet, he is obliged to crawl out through the exit. [Sidenote: The wonderful process of flower fertilization] The object of this elaborate device is as follows: In the entrance passageway is located the stigma (female organ), while in the exit passageway the male or pollen-bearing organ of the orchid is found. The bee visits several of these flowers consecutively, and, as he makes his exit from each flower, he bears away on his body a portion of the pollen, which is transferred to the stigma of the next flower visited; while the bee, being forced to go through a "plunge bath" before visiting another flower, acquires a fresh load of pollen in each case. This scheme is a certain means of securing fertilization or sexual reproduction, and positively prevents inbreeding (the fertilization of a flower by its own pollen). This is merely one of the wonderful adaptations of nature in the solution of the sex problem. [Sidenote: Reproduction among fishes] [Sidenote: Nature's wasteful methods]