v] NATURE OF PLANT-ANIMALS 157 



supplies of this element were obtained together with 

 nitrogen. In these circumstances, the expensive chlo- 

 rophyll apparatus ceased to be worth its upkeep and, 

 wearing out, proved to be too costly in nitrogen to be 

 replaced. Thus the organism, now devoid of chloro- 

 phyll, was reduced to a condition in which it obtains 

 directly from its environment as much carbon in 

 combined form as is of use to it and as much combined 

 nitrogen as it can get. It has become a saprophyte. 



Should this hypothesis of the origin of sapro- 

 phytism be established, C. roscoffensis and C. para- 

 doxa will rank high in interest among organisms as 

 suggesting the route along which far-reaching evo- 

 lution has travelled. In any case, it may be claimed 

 for our plant-animals that they have anticipated the 

 advice of Candide and live to cultivate their gardens. 



Both C. roscoifensis and C. paradoxa possess self- 

 sown, well-tended, highly productive gardens, and if 

 they could but learn how to bequeath packets of 

 vegetable seed to their descendants, they might lose 

 their animal characteristics altogether and become, 

 C. roscoffensis a green plant, and C. paradoxa a yellow- 

 brown plant. As it is, the garden has to be replanted 

 in the individuals of the successive generations and 

 so they remain plant-animals. 



