25° 



F. BORGESEN 



growing out at acute angles from the mother filaments and soon attaining the 

 same strength as these. 



In the upper part of the thallus the cells are of much variable length, 

 5 — 10 — 20 times as long as broad or even more. The diameter of the cells 

 varies from 50 — 100 ji being mostly 70 — 80 u~ 



The basal parts of the thallus have a different appearance. Here the cells 

 are much shorter, the filaments (Fig. 2 a) are irregularly bent and curved, and 

 much less regularly ramified; and furthermore we find here a great number of 

 rhizoids. These rhizoids serve for the most part to attach the plant to the 

 substratum but also to keep the whole thallus together as many of them fasten 



Fig. 2. Cladophora socialis Kiitz. Parts of plants showing ramification and formation of 



rhizoides. a c. 30 /i, b, c c. C5 /i- 



themselves to other filaments. The rhizoids are sometimes long, sometimes 

 short; in the long one cross walls are often present while the short ones have 

 no cross walls. They generally end in a small coralliform disc. There is no 

 cross wall separating the rhizoid from its mother cell. 



The wall of the filaments is thin in the young parts of the thallus, thick 

 and stratified in the older parts. 



By its ramification and mode of growth as well as by the fact that the 

 rhizoids are not cut off from their mother cells by cross walls this plant at the 

 first glance reminds rather much of Cladophoropsis, but it is of course easily 

 distinguished by the presence of cross walls at the base of the branches. 

 Furthermore it must be remembered that the formation of cross walls in the 

 filaments of Aegagropila takes place in the same way as f. i. in Cladophora, 



