200 F. KEEBLE AND F. W. GAMBLE. 



Bat, as we have already shown in Section IV, the alga in 

 its free state grows more actively when enabled to obtain its 

 uitroo-en from organic compounds (uric acid and urea) than 

 when " inorganic nitrogen " (nitrate) is supplied. 



Next, as to the mode of nutrition of the alga in its "Con- 

 voluta stage." 



Geddes (1879-1881) was the first to demonstrate that 

 Convolata gives off oxygen when exposed to light. He also 

 proved the presence of starch in the green cells, stating that 

 this substance is present always in small quantities. Oar 

 own experiments complete the proof that the green cells of 

 Convoluta photosynthesise carbohydrates. Thus, we have 

 shown that the green pigment of these cells is true chlorophyll 

 (op. cit., p. 377), and that starch, present in the green cells, 

 disappears in darkness and reappears when the animals are 

 bi'ought into the light. The photosynthetic activity of the 

 green cells having been demonstrated, the questions remain. 

 Does the animal receive a share of the elaborated carbo- 

 hydrate ? and, if so. How is the transference of this substance 

 from green cell to animal tissue effected ? 



Geddes has stated that Convoluta survives only a few 

 days' exposure to darkness, the implication being that when 

 photosynthesis is arrested death from starvation ensues. But 

 according to our experiments (op. cit. p. 375), if care is 

 taken with respect to the water supply Convoluta may live in 

 darkness for several weeks. 



Again, Geddes' statement that starch occurs in Convoluta 

 only in small quantities might be interpreted as meaning that 

 the product of photosynthesis is passed on to the animal as 

 soon as it is formed, and that only a small residue is accumu- 

 lated in the green cell. The observation, however, is incorrect, 

 for the green cells of Convoluta at certain times contain so 

 much starch as to give to the body when stained with iodine 

 a deep blue or blue-black colour. 



We have endeavoured to ascertain to what conditions the 

 variable amount of starch in the green cells is due. 



For this, samples of animals were collected twice daily 



