134 11 FE : OUTLINES OF GENERAL BIOLOGY 



some day become a disintegrative parasite, and it was probably 

 an unimportant niycf rhiza before it became a symbion. 



Every year adds to our knowledge of symbiotic linkages. Ac- 

 cording to Miss Kaynor and others, though there are dissentients 

 like Knudson. the success of the heather on poor or unready soil is 

 due to its intimate partnership with a fungus whose delicate 

 filaments spread from root to shoot, from leaf to flower, and even 

 into the seed. Many trees have a beneficial fungoid feltwork (my- 

 corhiza) closely associated with their roots. Everyone knows that 

 Leguminous plants, like clovers, lupins, and vetches, have in their 

 gall-like root-tubercles symbiotic bacteria by means of which they 



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Fig. 36. 



Commensalism or Mutually Beneficial External Partnership between a 

 Hermit-crab and Several Sea-Anemones. From a sj>ecimen. 



are able to fix the free nitrogen of the air. Thus plant joins hands 

 with plant, and nothing succeeds like symbiosis! 



Very abundant in the surface waters of the ocean are the micro- 

 scopic Radiolarians, with shells of extraordinary beauty, fashioned 

 crystal-wise out of flint, or spun of a transparent protein material 

 called acanthin. Now, there are some five thousand different species 

 of these Radiolarians, and as to the numbers of individuals, why, 

 there may be as many in a bucket of water as we can see of stars 

 on a clear night. May it not be that part of the success of these 

 Radiolarians is due to the fact that they all illustrate symbiosis? 

 Inside the clear living matter of these minute and for the most part 

 unicellular animals there are groups of still smaller single-celled 

 Alg.x" (zooxanthell.x') which are able to effect photo.synthesis. The 

 Algae or yellow cells, as they are called, utilise the carbon dioxide 

 made by the Radiolarian, which in turn benefits by the oxygen 

 hlxjrated by the partner-plants. So if the Radiolarian is not obtaining 

 sufficient extraneous food in the form of minute organisms captured 



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