112 



sponge and green alga is, considered from the point of view of the 

 use to the sponge, we cannot very well ansiver that qiiestioti, before 

 the problem, mentioned above, about the significance for the sponge 

 of the 0.^ secreted by the green alga in the light, has come to 

 solution : 



a. If the significance of that 0.^ is in fact so important, as was 

 thought possible above, we must conclude — notwithstanding the 

 fact, that the sponge continually destroys and digests numbers of 

 algae, and notwithstanding all other phenomena, which do not seem 

 to go together with a symbiosis — that the relation of sponge and 

 green alga, considered from the point of view of the use to the 

 sponge, is in fact a symbiosis, though this symbiosis is by no 

 means so complete as that of the Lichens. 



b. If, on the contrary, the significance of the 0^ secreted by the 

 alga is only of little importance, tve can conclude — whatever 

 may be the real cause of the dying of the algae in the sponge 

 tissue, weth&r it be the want of food of the sponge or (and) the 

 ^poisoning^^ of the algae by products o f metabolism o f the sponge — 

 we must conclude that, practically spoken, that so called symbiotic 

 relation of sponge and alga is in fact nothing but simply a process 

 of nutrition of the sponge, or, if you like, a very first transition 

 of a process of nutrition into a symbiosis. At any rate this always 

 counts for a sponge in darkness. 



For tve could state the following: 



The sponge continually imports green algae from, the surrounding 

 water into its amoebocytes {p. 50), where those algae then — it should 

 be explicitly mentioned — are killed a?id digested {p. Ill) by the 

 sponge only for a part, when circumstances are favourable; 

 while the rest of the algae can live on, photosynthesise and mul- 

 tiply {and will give their 0.^, produced in light, to the sponge 

 tissues (p. 93) — the only argument one can mention in favour 

 of the conceptio)! of symbiosis !). This favourable case is only realized 

 in sponges growing in light (p. 70 — 72) — for in light i y mo ') — 



1) This follows from p. 70 IV, p. 51, and p. 60-61, 59. In darkness i=^mo; so ia 

 light i > mo. 



