30 



this genus: 1. Chlorella vulgaris, 2. Chi. infusioimm, 3. ^^Chlorella 

 {Zoochlorella) parasitica Brandt ; Chlorophyll von Sjwngilla fuvia- 

 tilis, vielleicht identisch mit Chi. infusionum und wahrscheinlich 

 wahrend des individuellen Lebens durch Spongilla von aussen 

 aufgenommen. Isolirungsversuche nicht gelungen". And at last: 

 4. „Chi. (Zoochlorella) conductrix Brandt; Chlorophyll von Hydra, 

 Stentor, Paramaecium und wahrscheinlich von vielen anderen grü- 

 nen Thieren". 



In the first place I should mention the fact, that in botanical 

 literature of modern times the Chlorellae are no longer reckoned 

 among the Pleurococcaceae, but that Chlorellae and Pleurococcaceae 

 are considered to be two entirely separated groups (see Oltmanns 

 (47) 1905, Wille (69) 1911, and this paper pag. 33—34). 



But when we compare the definition Beljerinck gives for Chlo- 

 rella , and consequently for the symbiotic alga of the Spongillidae 

 as well, with my observations concerning this alga, we are struck 

 by the fact, that Beijerinck mentions paramylum, coloured brown 

 by I, to be a product of the photosynthesis, while, on the con- 

 trary, I found oildrops and never any carbohydrate that could 

 be stained by I. A thing of much more importance, however, is 

 the entirely diff'erent mode of reproduction I stated. 



The mode of reproduction of the green algae of the Spongillidae. 

 When studying the different forms of chloroplasts I immediately 

 observed, that in cells with double chloroplast both halves of 

 the latter were always symmetrically situated with respect to an 

 imaginary axis of the cell (Fig. 16, 17a). I also often found two 

 cells, each with a single chloroplast, which cells were connected 

 one with the other along a short distance of their wall, while 

 their chloroplasts were situated in the same way, now symme- 

 trically with regard to the common cell-wall (Fig. 22a). Conse- 

 quently, the last couple of cells seemed to be a stage of division 

 of the first cell with double chloroplast. This proved to be really 

 the case : once that my attention was drawn to this fact, I have 

 observed numerous different stages of division (Fig. 17 — 22). Some- 

 times I have also been able to follow the division of an alga — 



