179 



h. The export (e) of tlie algae from the sponge into the sur- 

 rounding water, an uncertain but probably not important 

 factor (p. 52, Fig. 76). 



c. The reduction (r) of the sponge tissue to a smaller volume, 

 a factor which in nature only occurs in autumn and then 

 might cause increase of the concentration of the algae in 

 the tissue (p. 52 — 53). 



d. The growth {g) of the sponge tissue, which in a long space 

 of time must strongly lower the concentration of the algae 

 in the tissue and which is more active in green sponges in 

 light than in colourless ones in darkness (p. 53). 



e. The intensity of multiplication {mu) of the algae, which in 

 sponge tissue in equal concentration of the algae is much 

 larger in light than in darkness, in light in a strong con- 

 centration larger than in a weak one, but in darkness in 

 both cases ± (p. 54—56, Table 9, 10). 



f. The mortality (mo) of the algae, which in sponge tissue in 

 equal concentration of the algae is much larger in darkness 

 than in light, in darkness in a weak concentration some- 

 what smaller than in a strong one, but in light in both 

 cases almost just as large (p. 56 — 62, Table 6, 8). 



14. By cultivating the sponges under such circumstances, that 

 the factors of import, export, reduction and growth were al- 

 most entirely excluded, we could show that the phenomena — 

 that green sponges grow colourless in darkness and colourless 

 sponges grow green in light — must be explained as being caused, 

 under these circumstances, by the combined action of the multi- 

 plication and the mortality of the „symbiotic" algae (p. 62 — 66, 

 Table 8). And we were able to prove, by means of the above 

 mentioned data concerning those two factors, why they must 

 cause those phenomena (p. 66 — 67). 



15. Next we have proved with the help of the above given 

 data concerning all 6 factors (import, export, reduction, growth, 

 multiplication and mortality) : I. Why in nature the Spongil- 

 lidae must contain such an amount of the various green and 

 colourless stages of the „symbiotic" algae in light and in dark- 



