18Ö 



ness, as we have experimentally stated, in short above sub 12 

 and in extenso on p. 46 — 48 sub 1 — 11. II. How in nature these 

 sponges keep up their „colour" (green or colourless), and how 

 both „colour"-types arise from each other. For, what happens 

 eg. to the number of green algae of a sponge under certain cir- 

 cumstances, in other words how the colour of the sponge is af- 

 fected, entirely depends upon the value which each of those 6 

 factors takes under these circumstances in the formula 



> 

 ^ + r + imi = e + r/ -f mo 



< 



the formula, which we have got to know as decisive for the 

 number of green algae of a sponge (p. 68 — 75). 



16. By a comparison of the behaviour of the „symbiotic" 

 algae when cultivated in sponge tissue and isolated in water, we 

 got to the following conclusion: In darkness the „symbiotic" as- 

 sociation of sponge and alga offers much less advantage to the 

 alga than a life free in the water, as in the sponge all algae 

 are destroyed (p. 77, 83, Table 10). In light, on the contrary, 

 that „symbiotic" association offers more advantage to the alga 

 than a life free in the water; that advantage, however, only 

 consists in the fact, that the sponge protects the alga against 

 destruction, eg. by enemies (p. 76 — 80, Table 10). The milieu — 

 the feeding milieu — , on the contrary, is in the sponge not at 

 all more favourable to the alga than in the water, neither in 

 light nor in darkness, but about just as favourable or even less 

 favourable (p. 77, 80—83, Table 9, 10). When further we know 

 that also in light algae are constantly destroyed in the sponge 

 — though less than in the water — , we must conclude, that 

 from the point of view of the use to the alga that association 

 with the sponge cannot be called at all a symbiosis in the mean- 

 ing of that of the Lichens (p. 84, 113 — 114). 



17. We could establish in 26 points the facts which bear upon 

 the question about the use of the „symbiotic" association (with 

 the alga) to the sponge (p. 84—95, Table 11—15). 



