38 SYMBIOGENES1S 



amphimixis and to genuine viability. " They toil not, 

 neither do they spin." They rely on new supplies turning up 

 as by Providence ; but they do not themselves cultivate and 

 turn into pasture lands the soil from which they draw. 

 Symbiotic in a sense the case of Convoluta may be, but it is 

 rather a one-sided and retrograde symbiosis to be distinguished 

 from progressive symbiosis. 



In progressive symbiosis the partial renunciation of their 

 individual independence by the partners, be they plantagens 

 or otherwise, favours the production of permanent physio- 

 logical and bio-economic values. The seasonal rhythm with 

 which the parasitic excursion of the rose-aphis recurs has a 

 parallel in the seasonal rhythm of plantagen activity in a tree, 

 but qualitatively speaking there is a great difference between 

 the two. 



The plantagens of the tree represent a case of vicarious 

 sacrifice, both as far as the domestic and the biological com- 

 munities are concerned. As Mr. Davidson says himself, if for 

 the majority of the plantagens the bud stage is the limit, 

 " they are merely humble workers, hewers of wood and drawers 

 of water for their gorgeously-attired sisters, who flaunt their 

 fine feathers in the sunshine." How can a similar degree of 

 symbiosis be shown to exist in the case of " the worst pest of 

 the garden" indulging in "reckless profusion" (of physio- 

 logical capital) on the one hand, and in wholesale destruction 

 of organic wealth on the other? The two cannot fairly be 

 compared. 



What is represented by Mr. Davidson as a mere gastro- 

 nomic whim, or as a mysterious craving for a change of diet, 

 is thus, in reality, a highly significant and deep-seated physio- 

 logical and symbiogenetic necessity exhibited by numbers of 

 plants and animals towards a reduction of surfeit and of 

 depredation as a pre-requisite to the re-establishment of sexual 

 reproduction. There is the case of the Rhine salmon and that of 

 the Adelie penguins fasting during the breeding period. Many 

 other examples occur among animals, as Prof. J. A. Thomson 



