Symbiosis

Symbiosis, a term originally employed by De Bary in 1879, for cases in which organisms of distinct species live together in such a condition of consortism or commensalism as to benefit both, in opposition to parasitism (q.v.), in which the advantage is all on one side. Etymologically, however, and perhaps as a matter of convenience, it might be well to expand the connotation of the term to include all forms of organic association - e.g. socialism, or the association of numerous individuals of one species, mutualism, and parasitism, especially as the two last-named seem connected by numerous intermediate cases. The two most striking instances of mutualist symbiosis are the alga-fungus association first pointed out by Schwendener in 1868 in the cases of lichens (q.v.), and the algal yellow-cells within the bodies of Radiolaria detected by Haeckel in 1870, and explained by Geddes in 1882. It is important to notice in the former case that the mutualist community of alga and fungus constituting the lichen can live in situations where neither can exist separately. In the latter case Geddes showed that the yellow cells had cellulose walls, were coloured by diatomin, evolved oxygen and formed starch when in sunlight, and absorbed carbon-dioxide and nitrogenous waste substances from the animal's body, thus performing both respiratory and quasi-renal functions for it and being nourished in return. He concludes "for a vegetable cell no more ideal existcnce can be imagined than that within the body of an animal cell of sufficient active vitality to manure it with abundance of carbonic anhydride and nitrogenous waste, yet of sufficient transparency to allow the free entrance of the necessary light. And, conversely, for an animal cell there can be no more ideal existence than to contain a sufficient number of vegetable cells, constantly removing its waste products, supplying it with oxygen and starch and being digestible after death."