William Thompson Sedgwick

“ Evidently the oxygen thrown off by the alga is precisely what the plant needs, and the carbonic acid and nitrogenous waste eliminated by the animal is most useful to the alga. Moreover, the algae gain the advantage of ready locomotion with their host, and the animal can go further into unfavorable media when stocked with algae ready to build up starches and sugary matters from carbonic acid and water. ”

“ If it can be proved that animal substance endowed with chlorophyl can, just as well as plant protoplasm similarly colored, break down carbonic acid and utilize its elements, then we remove the last formidable barrier between plant and animal protoplasm. ”

“ Here the colorless cells—of the root, let us say—are bound to live at the expense of the green cells in the stem and leaves. Yet we do not think of this as a parasitic event. The root-cell is rather a unit in a vast colony of units (cells) associated for mutual benefit. The green cell gets quite as much good from the root-cell as the latter gets from the green cell ”

“ In 1871 Cienkowski boldly announced his conviction that certain yellow cells, which, first pointed out by Huxley, had for some time attracted attention in the substance of radiolarians, were really no part of the animals themselves, but rather veritable algæ living in the animals. Haeckel had previously called them "liver-cells," and when starch was found in them he believed his view confirmed, as it is in the liver of the higher animals that glycogen—a form of starch—is constantly present. ”

“ He was able also to prove that this gas came from the associated algæ—specimens destitute of algæ giving off no oxygen whatever.
It is, therefore, now very certain that the yellow cells of radiolarians and the pigment-bodies of cœlenterates are in many cases true alga; living in the animal substance. ”

“ Geddes's work, when added to that of Cienkowski, the Hertwigs, and Brandt, makes this so clear that we are justified in fully accepting their theory, and in hereafter considering the association of certain chlorophyl-bearing plants with certain animals as an established fact. It has been proposed to apply to this association the term symbiosis, and to designate animals which are thus supplied with algoid messmates as "symbiotic." So much for the "yellow cells" and pigment-bodies of radiolarians and coelenterates. Dr. ”