35 



I should mention, however, that it might be possible, that our 

 fresh-water sponge will associate with quite different unicellular 

 algae in other countries, as I will point out afterwards (at the 

 end of chapt. VIII and chapt. IX). 



V. Green and colourless fresh- water sponges; under what 



circumstances they occur; the nature of their 



„symbiotic" algae. 



"When we examine under what circumstances the fresh-water 

 sponges occur, we find that, generally speaking, the green spon- 

 ges grow on places exposed to bright day-light — for instance on 

 the wooden lining of the lake bank — ; the colourless sponges^ 

 on the contrary, on places in darkness or in ttvilight — for instance 

 under bridges and landing places of steamers — . 



One might ask if the green and the colourless form could 

 not be two separate varieties of the sponge. This is not the case ; 

 for, as I will mention afterwards, green sponges prove to groiv 

 colourless in darkness and colourless ones prove to grotv green in 

 light (Table 8, p. 66), while moreover one may often find in nature 

 specimina partly green and partly colourless. 



I analyzed on a large scale the number and nature of the 

 symbiotic algae in fresh- water sponges by means of ravel prepa- 

 rations (Table 6 A, C). In that table (column 1 and 3) we see: 



1. In the green sponges in light as well as in the colourless ones 

 in darkness green as well as colourless chlorophyll corpuscles 

 (algae) occur. 



2. In the green sponges the green corpuscles are much more 

 numerous than in the colourless ones. 



3. In the green sponges the colourless corpuscles are somewhat 

 less numerous than in the colourless ones. 



4. In the green sponges the colourless corpuscles are much less 

 numerous than the green ones; in the colourless sponges they 

 are just as nunieroiis or still somewhat more numerous. 



I am speaking here about colourless chlorophyll corpuscles, in 

 other words, about a colourless form of the symbiotic algae. This 

 requires further explanation. 



