105 



sponge in light with regard to the total number of living (green) 

 algae present (p. 46 — 48, Table 6). 6. In nature the number of 

 dying algae (colourless ones with structure) in a colourless sponge 

 in darkness is larger than in the green sponge in light (p. 48); 

 this number (in colourless sponge) is almost equal to that, which 

 is continually imported into the sponge (p. 69 — 70), 7. If one culti- 

 vates green sponges in light in water from the conduit, the number 

 of colourless algae with structure generally appears to increase 

 (p. 95, point 26). 8. Isolated and cultivated in cultures, the algae 

 prove to remain living and green for months in light and in 

 darkness, and even to multiply (p. 40 — 41). 



Let us now see, to what conclusion regarding the cause of the 

 dying of the algae within the sponge — point I, 1 — 4 (p. 103 — 

 104) — we can come in connection with the facts, mentioned 

 here under II, 1 — 8. And let us then begin with the dying in 

 a sponge in darkness. 



As we see on the one side (point II, 5), that only so few 

 green algae die in a sponge in light and on the other hand 

 (point II, 3, 6) so many more in a sponge in darkness, we must 

 come to the conclusion, that in the last case the lack of light is 

 the reason of the so much increased mortality. So we immediately 

 try to find its cause: on the one side (point I, 1) in the sponge 

 cells killing the algae much more considerably from want of food 

 and (point I, 2) in the stronger „poisonous" influence of the 

 metabolism-products of the sponge in darkness, on the other hand 

 (point I, 3, 4) in lack of food and of 0.^ and in accumulation 

 of C 0^ in the algae themselves. However, we also know (point 

 II, 8) that without the sponge tissues the algae can live for 

 months in darkness and even multiply. Consequently, that lack 

 of light — with its supposed consequence of lack of food and 

 of O2 and accumulation of C 0^ in the algal cells — by itself 

 cannot possibly be the direct cause of the dying of the algae in 

 darkness. On the contrary, it proves necessary for that manifold 

 dying of the algae to be in darkness in an actively living sponge 

 (point II, 6, 3, 2, cf. Table 10). The only and at the same 

 time most general solution would be therefore, that on the one 



