109 



When we look over the results obtained, we might conclude the 

 following causes for the dying of the algae in the sponge tissue: 

 A. In light in fact only ^killing from want of food" (point 1, 1^, 

 and such of the (few) algae, the power of resistance of which is 

 somewhat weakened already for some or other reason; but not 

 „poisoning" by products of metabolism (point I, 2) nor lack of 

 food, lack of 0^, and accumulation of COr, in the algae them- 

 selves (point I, 3, 4). B. In darkness either y,killing from want 

 of food"" (point I, 1) — perhajjs even stronger now — or (and) 

 y^'poisoning'' by products of metabolism (as reaction of defence of 

 the sponge against a foreign intruder) (p>oint I, 2), and such 

 again of algae, the p>ower of resistance of which has certainly 

 weakened noiv much more, iti consequence of lack of food or of 

 0.^ and accumulation of CO.^^^ (point I, 3, 4). 



For the present a more detailed conclusion cannot be given; 

 more data are required for that, among others about the problem 

 if there is really question about lack of 0^ — with all its con- 

 sequences, as for instance increased want of food — in the tis- 

 sues of a sponge in darkness. 



Let us now pay attention to the two points {/x, /3, p. 108), re- 

 garding this last problem and which are so important, because 

 they give us an insight into the significance, which the 0.^, se- 

 creted by the green algae in light within the sponge tissue, might 

 have for the life of the sponge. One cannot say, that the con- 

 clusion, made in connection with those points oc and (o, quite 

 satisfies us. 



The hypothesis, that in lack of 0.^ the katabolic phase of the 

 metabolism will have quite another course (than in abundance of 

 0.,) and consequently will cause an increased want of food — 

 as is given on p. 98 and 103 sub I, 1 — may be right in general, 

 it seems a bit far-fetched to consider this hypothesis applicable 

 to our case of a sponge in darkness. Certainly, the sponge in 

 darkness will possess a much smaller quantity of 0^ in its tis- 

 sues than the green sponge in light. But is there really lack of 

 O., , while sponges have even an extremely strong circulation of 



