40 



type II (hypothetical). 



in poorer feeding solution the algae become colourless. 



in rich feeding solution the algae remaio green, 

 type III (Chlorella, Stichococcus, Chlorococcum from Xanthoria). 



in poorer feeding solution 



in rich feeding solution 



type IV (hypothetical), 



in poorer feeding solution 



in rich feeding solution 



the algae remain green. 



the algae become colourless. 



A poor or a rich feeding solution here always means a solution 

 poor or rich in organic feeding substances. 



To decide to which type the green symbiotic alga of our 

 sponges belongs, it was isolated from the sponge tissues and cul- 

 tivated in light and in darkness in various feeding solutions. I 

 will not treat these cultures here at large ; one can find a de- 

 tailed description in Table 4 A, B. 



The result we infer from these cultures is, among others, that 

 the symbiotic algae remain green and multiply by means of 

 green descendants under all circumstances. However, we had not 

 yet examined every imaginable combination of feeding in the in- 

 organic and organic feeding solutions used here; on the con- 

 trary, some chief combinations only. So it might be possible 

 still, that a fresh-water sponge offered exactly such a combina- 

 tion of food to its algae, that they did lose their green colour in 

 darkness or in light. So we had to study this possibility as well, 

 for which a feeding solution was required, differing as little as 

 possible as to composition and concentration from the one sur- 

 rounding the algae in the living sponge. I got this solution (the 

 so called diluted and concentrated liquid from a sponge) in the 

 way described on pag. 11. The result inferred from these cul- 

 tures is quite the same as that from the preceding cultures, as 

 Table 4 A, B shows: 



1. The isolated green symbiotic algae of the Spong illidae, whether 

 cultivated in light or in darkness in poor or in rich organic 

 feeding solutions^ even in liquid pressed from a sponge, remain 



