SYMBIOLOGY — THE BIOLOGICAL RELATIONSHIPS OF ORGANISMS 1 29 



pie, the cells are unquestionably of homogeneous origin; whereas in the 

 lichen group we know for a certainty that the cells are of heterogeneous 

 origin (alga and fungus). It is highly probable that some of the living 

 elements of the cells of higher plants are of heterogeneous origin, like- 

 wise those of such animals as the chlorophyll bearing Hydra viridis and the 

 chlorophyll bearing amebas. 



9. Whether or not the cells resulting from septation remain free or 

 uhcombined as in the protozoa, bacteria, single-celled algae, etc., or united 

 as in many-celled plants and animals, is incidental in the order of evolu- 

 tion. In both cases septation is cyclical, that is, jt continues until the 

 septating power is exhausted and death of the entire somatic cell associa- 

 tion follows. In both cases extinction of the cyclical and individualistic 

 and autonomous cell groupings is prevented by spore formation and by 

 the gametic fusion of certain specialized cells. 



10. All evidence points to the biological fact that as the association 

 of ceUs of the same kind became closer and closer physically, there was 

 developed a corresponding increase in the biological and physiological 

 interdependence of the cells, with a gradual reduction or lessening of the 

 individualism or independence of the cells. In the lowest many-celled 

 plants and animals, a single cell still retains the power to develop into a 

 new individual, as in Saccharomyces, diatoms, desmids, water net, lower 

 filamentous algas, streptococci, etc. As the cell grouping became more and 

 more intimate and interdependent biologically, the individual cell could 

 no longer dissociate itself and develop into a new group. The individual 

 cell can only septate while in contact or biological association with its 

 fellows. Fragments representing a variable number of cells still in biologi- 

 cal association, of certain lower plants and animals, as among the algae, 

 the fungi, the hchens, hydras, sponges, liverworts, etc., etc., could still 

 develop into new organisms. Finally the somatic cells of the organism 

 lost wholly the power of developing into a new individual, no matter how 

 large the dissociated fragment might be, as is the case in all higher 

 animals and in many of the higher plants. 



11. The Uving inclusions of the cell are even more intimately interde- 

 pendent biologically (somatically) than are the cells composing the indi- 

 vidual, and it is therefore not surprising to find it very diflacult, if not 

 absolutely impossible, to induce- such plasmic cell units to multiply when 

 dissociated form the mother cell. Amyloplastids, chloroplastids and 

 leucoplastids have been seen to increase numerically outside of the cell in 

 the hanging drop but so far no one has succeeded in inducing such nu- 

 merical increase to proceed to any very considerable cell mass formation. 

 The indications are that any such numerical increase is more apparent 

 than real. That is, the plastids which were aheady present in the embryonic 



