v] NATURE OF PLANT-ANIMALS 147 



jecture is confirmed by experiment. Comparative 

 cultures of the free stage of the infecting organism 

 have demonstrated that the alga flourishes better when 

 supplied with nitrogen in the form of uric acid than 

 when it is supplied with a nitrate (potassium nitrate). 

 Thus our argument brings us to the following 

 position : We have evidence that the infecting 

 organism increases rapidly as soon as it gains access 

 to the body of the plant-animal. We know that it 

 is able to utilise organic nitrogen compounds such 

 as uric acid for the construction of its proteins. We 

 know, further, that no apparatus for the removal of 

 waste nitrogen compounds, uric acid, urea, etc., occurs 

 in the bodies of C. roscoffensis or C. paradoxa. The 

 conclusion forces itself upon us that the green and 

 yellow-brown cells in the bodies of their respective 

 hosts obtain access to and utilise the stores of waste 

 nitrogen-compounds accumulated therein. Or, to 

 put the same idea in another way, green cells and 

 yellow-brown cells constitute the excretory organs 

 of C. roscoffensis and of C. paradoxa respectively. 

 The plants flourish in the bodies of these animals 

 because there they discover large accumulations of 

 waste nitrogen compounds: the animals, looking to 

 the algse to come and take charge of the work of 

 getting rid of these waste substances, have ceased 

 to construct any excretory apparatus whatever. 

 Hence it is not surprising that, when the alga? fail 



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