i 4 SYMBIOSIS 



unfavourable to the plant. For the numbers of " plant- 

 carnivora " are kept down by the inordinate appetites of the rank 

 in-feeders and rank carnivores, which are thus as " executioners " 

 in the service of the plant (by whom they are ultimately main- 

 tained). It is not to be denied, therefore, that, owing to the 

 disobedience to the law of Symbiosis, there is a need of " execu- 

 tioners " in the world. It is customary to refer to the respective 

 phenomena by saying that there exist " complex and unexpected 

 checks " amongst organisms " which have to struggle together " 

 (Evolution, by Geddes and Thomson, p. 153). A typical 

 example is generally adduced from Darwin's Origin, chap. III. 

 It is as follows : " Red clover depends for fertilisation upon the 

 humble-bees, these upon immunity from the attacks of field 

 mice, and thus indirectly upon the number of cats." 



Such instances of checks and counter-checks, interesting 

 enough by themselves, have deluded many a reader into facile 

 acceptance of the belief in the blind struggle of organism against 

 organism in Nature, whilst, in my view, they merely illustrate 

 the eternal difference between right and wrong. I should merely 

 say that even cats may be of indirect importance in Symbiosis, 

 namely as " executioners," decimating the " plant-carnivora." 



It is of some little interest in this connection to examine 

 Darwin's own account of this case. He says : 



" I am tempted to give one more instance showing how plants and 

 animals, remote in the scale of nature, are bound together by a web of 

 complex relations." 



(Follow examples of the absolute dependence of some plants 

 upon insect fertilisation, as that of Lobelia fulgens, of our 

 orchidaceous plants, of viola tricolour, and of clover.) 

 " Humble-bees alone visit red clover, as other bees cannot reach 

 the nectar." (Follows the case of the dependence of clover upon 

 cats.) 



'Hence it is quite credible (Darwin concludes), that the presence of a 

 feline animal in large numbers in a district might determine through the 

 intervention first of mice and then of bees, the frequency of certain flowers 

 in that district." 



While Darwin's conclusion is correct so far as it goes, I am of 

 opinion that it is nevertheless inadequate because it fails to make 

 us realise the nature of the relations and checks existing between 

 organisms in the web of life. Mere temporary " frequency " 

 of a species in a district tells us little about its real chance of 



