114 PLANT-ANIMALS [CH. 



for the hypothesis, suggested independently by 

 Schimper and Lankester, which we have already 

 outlined as to the composite nature of higher green 

 plants. The algal cells of C. roscoffensis are on 

 the road which leads to complete loss of inde- 

 pendence. In the higher green plant this loss is 

 complete. The green cells of C. roscoffensis lose 

 cell-wall and nucleus, but retain some colourless 

 protoplasm ; the green elements of the flowering 

 plant if they are regarded as the descendants of 

 originally free algse have lost everything except the 

 photosynthesising organs the chloroplasts. 



But a wide gap remains between the state of 

 affairs in C. roscoffensis and that in the higher green 

 plant. Sooner or later C. roscoffensis destroys and 

 digests its green cells, and none of them, nor any 

 colourless representatives of the green cells, pass into 

 the egg-cells ; whereas the higher green plants pro- 

 vide for the future crop of chloroplasts in their 

 descendants by transmitting colourless rudiments of 

 the chloroplasts to their egg-cells. 



An adult C. roscoffensis is a complex of two 

 organisms one, the colourless animal, the other, the 

 chloroplast-remainders of the original, green, nucle- 

 ated, algal cells. In its case, unlike that just imagined 

 for the green plant, the synthesis is not a permanent 

 one. It endures but for the lifetime of the animal 

 and has to be recommenced in every larval Convoluta. 



