in] GREEN CELLS OF CONVOLUTA 93 



starch into fat present any difficulty to vegetable 

 cells. For example, in many trees, the tissues of the 

 trunks contain, in autumn, large stores of starch ; as 

 winter advances the starch is replaced by oil or fat, 

 and, again, when spring arrives, the oil gives place 

 once more to starch. It is of course open to us to 

 suppose that, just as the sugar formed photosyn- 

 thetically by the green cells of a leaf is translocated 

 as fast as may be through the tissues of the leaf-stalk 

 and stem to meet the demands of the colourless cells 

 of the plant which depend for their food supplies on 

 the activity of the green cells, and just as the starch 

 which appears in the green cells of the leaf represents 

 only the surplus which is stored temporarily in a 

 convenient form to be changed to sugar and dis- 

 tributed later on ; so, in C. roscoffensis, the photo- 

 synthesised sugar streams away as such to the 

 colourless cells of the animal, only the surplus 

 being stored as starch. 



Whether it travels as sugar or, as the former 

 observations seem to indicate, as fat, there is no 

 doubt that the organic, carbon-containing food- 

 material, produced photosynthetically by the green 

 cells of C. roscoffensis, serves for the nutrition of the 

 animal's tissues. 



Indeed, as we show presently, unless the green 

 cells are present in the body of the animal, and 

 unless they increase and multiply therein, the animal 

 does not grow at all. 



