66o 



NA TURE 



[November 3, 1923 



(of which some thirty species are known), and (6) that 

 due to animal cell - products known as luciferin and 

 ludferase which are secreted and expelled at intervals, 

 in response to a stimulus, from two kmds of gland cells, 

 the secretions, when mixed, producing light. 



Portieres Hypothesis. 

 The numerous cases in which symbiosis occurs in 

 Nature have naturally led some biologists to ask if 

 symbiosis is not a phenomenon of general significance, 

 and perhaps essential, in living organisms. In this 

 connexion reference must be made to the hypotlK-sis 

 advanced by Portier (1918), because it formulates 

 extreme views. On faulty premises he built up an 

 hypothesis that may be likened to a house of cards. 

 He divides living organbms into two groups, autotrophic 

 (bacteria only) and heterotrophic (all plants and 

 animals), according as they are provided or not with 

 symbionts. According to Portier, the mitochondria 

 that are present in all plant and animal cells are 

 symbionts. Space precludes further consideration of 

 the subject here. 



Conclusion. 



The term " symbiosis " denotes a condition of 

 conjoint life existing between different organisms that 

 in a varying degree are benefited by the partnership. 

 The term " symbiont," strictly speaking, applies equally 

 to the partners ; it has, however, come to be used also 

 in a restricted sense as meaning the microscopic 

 member or members of the partnership in contra- 

 distinction to the physically larger partners, which are 

 conveniently termed the " hosts " in conformity with 

 parasitological usage. 



The condition of life defined as symbiosis may be 

 regarded as balancing between two extremes — complete 

 immunity and deadly infective disease. A condition of 

 perfect symbiosis or balance is realised with comparative 

 rarity because of the many difficulties of its establish- 

 ment in organisms that are either capable of living 

 independently or are incapable of resisting the invasion 

 of organisms imperfectly adapted to communal life. 

 In these respects the conclusions of Bernard and 

 Magrou in relation to plants apply equally to animals. 

 It is difficult to imagine that symbiosis originated other- 

 wise than through a preliminary stage of parasitism on 

 the part of one or other of the associated organisms, the 

 conflict between them in the course of time ending in 

 mutual adaptation. It is, indeed, probable that some 

 supposed symbionts may prove to be parasites on 

 further investigation. 



In perfect symbiosis the associated organisnis are 

 <<> ' adapted to a life in common. In parasitism 



th fadaptiition varies greatly ; itmayapproerh 



symbiotic conditions on one hand, or range to \ 

 ing point on the other by leading to the do 

 the organism that is invaded by a highly pat) 

 animal or vegetable disease agent. There is no d< : 

 boundary l>etween symbiosis and parasitism. The 

 factors governing immunity froni '^vtnJ.ionts or parasites 

 are essentially the same. 



No final conclusions can a* \ri i>i reached v ' 



ing the function of symbionts in many invert- 

 animals, owing to our ignorance of the ph\ i 1 i d 

 processes in the associated organisms. The ihm ti^.i- 

 tion of these problems is one fraught with difficulties, 

 which we must hope will be surmounted. 



New knowledge is continually being acquired, and 

 a glance into new and even recent publications shows 

 that symbionts have been repeatedly seen and inter- 

 preted as mitochondria or chromidia. Thus in Aphis 

 the long-known pseudovitellus has been shown to 

 contain symbiotic yeasts by Pierantoni and Sul^, 

 independently and almost simultaneously (1910) ; 



Buchner(i9i4) has demonstrated symbiotic lumini * 



fungi in the previously well-studied pyrosomes, ! 

 identifying (1921) as bacterial symbionts the iniiu- 

 chondria found by Strindberg (19 13) in his work 

 on the embryology of ants. The increasing number 

 of infective diseases of animals and plants, more- 

 over, which have been traced, especially in recent 

 years, to apparently ultramicroscopic organisms, can- 

 not but suggest that there may exist ultramicroscopic 

 symbionts. 



From the foregoing summary of what is known 

 to-day of symbiosis we see that it is by no means 

 so rare a phenomenon as was formerly supposed. 

 Symbiosis occurs frequently among animals and plants, 

 the symbionts (algae, fungi, bacteria) becoming in some 

 cases permanent intracellular inhabitants of their 

 hosts, and at times being transmitted from host to 

 host hereditarily. Among parasites, non-patlv 

 and pathogenic, we know of cases wherein hert<. 

 transmission occurs from host to host. 



It is evident that we are on the threshold of further 

 discoveries, and that a wide field of fruitful research 

 is open to those who enter upon it. In closing, it seems 

 but fitting to express the hope that British workers 

 may take a more active part in the elucidation of the 

 interesting biological problems that lie before us in the 

 study of symbiosis and the allied subject of parasitism. 



Crete as a Stepping-Stone of Early Culture : some New Lights.^ 

 By Sir Arthur Evans, F.R.S. 



nPHE unique geographical position of Crete, lying 

 ■* almost midway between Europe, Asia, and 

 Africa, marked it as the point where the primitive 

 culture of Europe was first affected by that of 

 the older civilisations of Egypt and the East. But 

 geographically it belonged in late geological times to 

 Anatolia, being separated from Europe by the irruption 



• w' A*>ndKe^ *»« « lecture deU\-ered before SecUon H (AnUuopology) of 

 the Bntish AssoctaUoa at Liverpool on September i8. 



NO. 2818, VOL. 112] 



of an arm of the Miocene Sea which later became the 

 iEgean. Thus the fauna of Crete show nearer con- 

 nexions with Asia Minor, as, for example, the Cretan 

 wild goat ; and this affinity is still reflected in its 

 Neolithic culture, of which at Knossos in places we 

 have a mean thickness of some 6J metres (23J feet) 

 as compared with about 5J metres (19 feet) for the 

 whole of the superincumbent strata. 



The builders of the Great Palace had themselves 



