— 175 — 



The thickness is about 0-4 ^, the length may reach about 40 t u. 

 Finding places: Birkerød Sø, Bastrup Sø, Bagsværd Sø, Bure Sø 

 and 6 ponds in North Sealand. 



Zacharias [1903 pag. 593] already apprehends that the bristles 

 are a buoyancy apparatus, and my investigations have only con- 

 firmed this result. I shall here particularly mention my observa- 

 tions as to the rigidity and elasticity of the bristles. If they were 

 quite soft they could not be of any avail in opposing the rate of 

 sinking, but when they are rather rigid and elastic, the friction will 

 be much increased; and supposing this to be their function, their 

 arrangement seems also to be very suitable to the purpose. Parti- 

 cularly the bristles projecting in right angles to the plane of the 

 coenobium seem to be fixed in an effective manner; for it is 

 evident that the coenobia are most exposed to sink when they are 

 in a vertical position, and that is justly what these tufts of brist- 

 les will prevent. Moreover the bristles at the marginal cells will 

 also be efficient when the coenobia are in the mentioned posi- 

 tion, the bristles at the points of the cells diverging from one 

 another in different directions and not only projecting in the plane 

 of the coenobia. 



This may perhaps be the place to mention the Pediastrum 

 biradiatum Meyen, a plankton-form I have several times had in 

 my cilia-staining preparations but without being able to find the 

 least vestige of bristles at it. The explanation is perhaps that the 

 cell processes at this species are longer than those of the other 

 species and moreover end in forked branches ; perhaps they suffice 

 as buoyancy apparati. 



At last I have to express my heartiest thanks to my teachers 

 Prof. Eug. Warming, Dr. L. Kolderup Rosenvinge and Dr. G. Wesen- 

 berg-Lund for the interest they have taken in my researches and 

 the support they have proved to me; and finally also my best 

 thanks to Prof. V. A. Poulsen for his useful advices and sugge- 

 stions. 



Litte ratu re. 



R. Ghodat 1902: Les algues vertes de la Suisse in Beiträge zur Kryptogamen- 



flora der Schweiz. Bern. 

 G. Kleb s 1886: Organisation der Gallerte bei einigen Algen und Flagellaten. 



Untersuch. Bot. Inst. Tübingen II. 



