ECOLOGICAL 133 



mental. A society always serves as a shield sheltering the individual 

 in some measure from the external sifting, and allowing of the 

 emergence and testing of variations and experiments which would 

 have little chance in an entirely individualistic struggle for existence. 

 This, as in human societies, sometimes leads to the survival of the 

 biologically undesirable, sometimes verging on the pathological. 



SYMBIOSIS 



'his rather fine word — symbiosis — which literally means living 

 ftogether, was first used in 1879 by the botanist De Bary to 

 [describe the partnership which he so much aided to demonstrate 

 fin lichens. For these curious plants, after long controversies before 

 land after that time, have been conclusively shown to be not the 

 [distinctive group of cryptogamic plants they seemed, but a compo- 

 ^site of others, a dual association of minute Algae entangled in the 

 leshes of a fungoid felt work. The Algae have chlorophyll and are 

 [therefore able to build up carbon compounds in photosynthesis 

 [like other green plants. In most lichens the partnership is very 

 [intimate, and, as one might say, perfect ; but there are many grada- 

 jtions connecting these with somewhat rough-and-ready combina- 

 jtions. In most cases, however, there is no doubt that the symbiosis 

 mutually beneficial. The Alga utilises the water and salts which 

 |the fungus absorbs from the weathering surface of the rock or the 

 lecaying surface of the branch. The Fungus, on the other hand, 

 m utiHse some of the organic matter that is elaborated by the 

 other members of the firm. One of the puzzles is the way in which a 

 balance is struck and maintained between the two parties. It must 

 be an automatically working pact, and in illustration of the way in 

 which this is elaborated in some forms, we may note how Darbishire 

 has lately traced the regular separation of the fungoid filaments 

 to form a characteristic opening above the Alga-patches, thus 

 furnishing them with what are practically stomata, though not of 

 any familiar build. 



One would like to see the clear and pleasant term symbiosis 

 restricted to a usage as precise as possible. It means a mutually 

 beneficial internal partnership between two organisms of different 

 kinds. The fact of "mutual benefit" serves, as well as one can expect, 

 to exclude parasitism, where the advantages, in typical cases at 

 least, are all on one side. The adjective "internal" serves to exclude 

 commensalism, an externally mutually beneficial partnership, 

 such as that between a hermit-crab and the sea-anemones it carries. 

 But what began as symbiosis may sink into parasitism, and what 

 began as parasitism may rise into symbiosis. Thus the fungus that 

 lives in intimate partnership with ling-heather may conceivably 



